{"id":4100,"date":"2021-02-01T11:28:38","date_gmt":"2021-02-01T03:28:38","guid":{"rendered":"https:\/\/www.gbase8.cn\/?p=4100"},"modified":"2021-02-01T14:25:15","modified_gmt":"2021-02-01T06:25:15","slug":"gbase-8a%e6%89%a7%e8%a1%8c%e8%ae%a1%e5%88%92%e4%bb%8e%e7%ae%80%e5%8d%95%e5%88%b0%e5%a4%8d%e6%9d%82%e7%94%a8%e4%be%8b%e8%ae%b2%e8%a7%a3","status":"publish","type":"post","link":"https:\/\/www.gbase8.cn\/en\/4100","title":{"rendered":"\u5357\u5927\u901a\u7528GBase 8a\u6267\u884c\u8ba1\u5212\u4ece\u7b80\u5355\u5165\u95e8\u5230\u590d\u6742\u7528\u4f8b\u8bb2\u89e3"},"content":{"rendered":"\n<p>\u672c\u6587\u9488\u5bf9GBase 8a\u6570\u636e\u5e93\u96c6\u7fa4\u7684\u6267\u884c\u8ba1\u5212\u529f\u80fd(Explain)\uff0c\u91c7\u7528\u4ece\u7b80\u5355\u5165\u95e8\u5230\u590d\u6742\u7528\u4f8b\u8bb2\u89e3\u5e38\u7528SQL\uff0c\u9010\u6b65\u89e3\u8bfb\u6267\u884c\u8ba1\u5212\u7684\u4f7f\u7528\u65b9\u6cd5\uff0c\u5305\u62ec\u5355\u8868\u805a\u5408group, 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class=\"ez-toc-link ez-toc-heading-10\" href=\"https:\/\/www.gbase8.cn\/en\/4100\/#%E3%80%90%E5%88%9D%E3%80%91%E5%8D%95%E8%A1%A8count\" >\u3010\u521d\u3011\u5355\u8868count(*)<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-11\" href=\"https:\/\/www.gbase8.cn\/en\/4100\/#%E3%80%90%E5%88%9D%E3%80%91%E5%8D%95%E8%A1%A8%E7%AE%80%E5%8D%95%E6%9F%A5%E8%AF%A2\" >\u3010\u521d\u3011\u5355\u8868\u7b80\u5355\u67e5\u8be2<\/a><ul class='ez-toc-list-level-3' ><li class='ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-12\" href=\"https:\/\/www.gbase8.cn\/en\/4100\/#%E6%97%A0%E8%BF%87%E6%BB%A4%E6%9D%A1%E4%BB%B6\" >\u65e0\u8fc7\u6ee4\u6761\u4ef6<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-13\" href=\"https:\/\/www.gbase8.cn\/en\/4100\/#%E5%B8%A6%E5%8D%95%E4%B8%AA%E8%BF%87%E6%BB%A4%E6%9D%A1%E4%BB%B6\" >\u5e26\u5355\u4e2a\u8fc7\u6ee4\u6761\u4ef6<\/a><\/li><li class='ez-toc-page-1 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href=\"https:\/\/www.gbase8.cn\/en\/4100\/#%E3%80%90%E5%88%9D%E3%80%91%E5%8D%95%E8%A1%A8%E5%85%A8%E9%83%A8%E8%81%9A%E5%90%88GROUP\" >\u3010\u521d\u3011\u5355\u8868\u5168\u90e8\u805a\u5408GROUP<\/a><ul class='ez-toc-list-level-3' ><li class='ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-18\" href=\"https:\/\/www.gbase8.cn\/en\/4100\/#%E9%9A%8F%E6%9C%BA%E5%88%86%E5%B8%83%E8%A1%A8\" >\u968f\u673a\u5206\u5e03\u8868<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-19\" href=\"https:\/\/www.gbase8.cn\/en\/4100\/#Hash%E5%88%86%E5%B8%83%E8%A1%A8\" >Hash\u5206\u5e03\u8868<\/a><ul class='ez-toc-list-level-4' ><li class='ez-toc-heading-level-4'><a class=\"ez-toc-link ez-toc-heading-20\" href=\"https:\/\/www.gbase8.cn\/en\/4100\/#%E8%81%9A%E5%90%88%E5%88%97%E4%B8%8D%E6%98%AF%E5%88%86%E5%B8%83%E5%88%97\" >\u805a\u5408\u5217\u4e0d\u662f\u5206\u5e03\u5217<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-4'><a class=\"ez-toc-link 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href=\"https:\/\/www.gbase8.cn\/en\/4100\/#%E5%A4%8D%E5%88%B6%E8%A1%A8-2\" >\u590d\u5236\u8868<\/a><\/li><\/ul><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-29\" href=\"https:\/\/www.gbase8.cn\/en\/4100\/#%E3%80%90%E5%88%9D%E3%80%91UNION%E6%93%8D%E4%BD%9C\" >\u3010\u521d\u3011UNION\u64cd\u4f5c<\/a><ul class='ez-toc-list-level-3' ><li class='ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-30\" href=\"https:\/\/www.gbase8.cn\/en\/4100\/#2%E4%B8%AA%E9%9A%8F%E6%9C%BA%E5%88%86%E5%B8%83%E8%A1%A8%E5%81%9Aunion\" >2\u4e2a\u968f\u673a\u5206\u5e03\u8868\u505aunion<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-31\" href=\"https:\/\/www.gbase8.cn\/en\/4100\/#2%E4%B8%AAHash%E5%88%86%E5%B8%83%E8%A1%A8%E5%81%9Aunion\" >2\u4e2aHash\u5206\u5e03\u8868\u505aunion<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-32\" href=\"https:\/\/www.gbase8.cn\/en\/4100\/#1%E4%B8%AAHash%E5%92%8C1%E4%B8%AA%E9%9A%8F%E6%9C%BA%E5%88%86%E5%B8%83%E8%A1%A8union\" >1\u4e2aHash\u548c1\u4e2a\u968f\u673a\u5206\u5e03\u8868union<\/a><\/li><\/ul><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-33\" href=\"https:\/\/www.gbase8.cn\/en\/4100\/#%E3%80%90%E4%B8%AD%E3%80%91%E5%B8%A6%E5%8D%95%E7%BA%AFcount%EF%BC%88%EF%BC%89%E7%9A%84union\" >\u3010\u4e2d\u3011\u5e26\u5355\u7eafcount\uff08*\uff09\u7684union<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-34\" href=\"https:\/\/www.gbase8.cn\/en\/4100\/#%E3%80%90%E4%B8%AD%E3%80%91%E5%B8%A6%E8%81%9A%E5%90%88GROUP%E7%9A%84union\" >\u3010\u4e2d\u3011\u5e26\u805a\u5408GROUP\u7684union<\/a><ul class='ez-toc-list-level-3' ><li class='ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-35\" href=\"https:\/\/www.gbase8.cn\/en\/4100\/#2%E4%B8%AA%E9%9A%8F%E6%9C%BA%E5%88%86%E5%B8%83%E8%A1%A8%E8%81%9A%E5%90%88%E7%BB%93%E6%9E%9C%E7%9A%84union%E3%80%82\" >2\u4e2a\u968f\u673a\u5206\u5e03\u8868\u805a\u5408\u7ed3\u679c\u7684union\u3002<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-36\" href=\"https:\/\/www.gbase8.cn\/en\/4100\/#2%E4%B8%AAHash%E5%88%86%E5%B8%83%E8%A1%A8%E8%81%9A%E5%90%88%E5%8C%85%E5%90%ABHash%E5%88%86%E5%B8%83%E5%88%97%E7%9A%84union\" >2\u4e2aHash\u5206\u5e03\u8868\u805a\u5408\u5305\u542bHash\u5206\u5e03\u5217\u7684union<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-37\" href=\"https:\/\/www.gbase8.cn\/en\/4100\/#%E9%9A%8F%E6%9C%BA%E5%88%86%E5%B8%83%E8%A1%A8%E5%92%8CHash%E5%88%86%E5%B8%83%E8%A1%A8%E5%8C%85%E5%90%AB%E5%9C%A8%E8%81%9A%E5%90%88%E5%88%97%E7%9A%84union\" >\u968f\u673a\u5206\u5e03\u8868\u548cHash\u5206\u5e03\u8868\u5305\u542b\u5728\u805a\u5408\u5217\u7684union<\/a><\/li><\/ul><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-38\" href=\"https:\/\/www.gbase8.cn\/en\/4100\/#%E3%80%90%E5%88%9D%E3%80%91UNION_ALL_%E6%93%8D%E4%BD%9C\" >\u3010\u521d\u3011UNION ALL \u64cd\u4f5c<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-39\" href=\"https:\/\/www.gbase8.cn\/en\/4100\/#%E3%80%90%E4%B8%AD%E3%80%912%E8%A1%A8join%E6%93%8D%E4%BD%9C\" >\u3010\u4e2d\u30112\u8868join\u64cd\u4f5c<\/a><ul class='ez-toc-list-level-3' ><li class='ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-40\" href=\"https:\/\/www.gbase8.cn\/en\/4100\/#Hash%E5%88%86%E5%B8%83%E8%A1%A8%E4%B8%94join%E5%88%97%E4%B8%BAHash%E5%88%86%E5%B8%83%E5%88%97\" >Hash\u5206\u5e03\u8868\u4e14join\u5217\u4e3aHash\u5206\u5e03\u5217<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-41\" href=\"https:\/\/www.gbase8.cn\/en\/4100\/#Hash%E5%88%86%E5%B8%83%E5%A4%A7%E8%A1%A8%E5%92%8C%E9%9A%8F%E6%9C%BA%E5%88%86%E5%B8%83%E5%A4%A7%E8%A1%A8JOIN\" >Hash\u5206\u5e03\u5927\u8868\u548c\u968f\u673a\u5206\u5e03\u5927\u8868JOIN<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-42\" href=\"https:\/\/www.gbase8.cn\/en\/4100\/#2%E4%B8%AA%E5%A4%A7%E7%9A%84%E9%9A%8F%E6%9C%BA%E5%88%86%E5%B8%83%E8%A1%A8%E5%81%9AJoin\" >2\u4e2a\u5927\u7684\u968f\u673a\u5206\u5e03\u8868\u505aJoin<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-43\" href=\"https:\/\/www.gbase8.cn\/en\/4100\/#%E5%A4%A7%E7%9A%84%E9%9A%8F%E6%9C%BA%E5%88%86%E5%B8%83%E8%A1%A8%E5%92%8C%E5%B0%8F%E7%9A%84%E9%9A%8F%E6%9C%BA%E5%88%86%E5%B8%83%E8%A1%A8%E5%81%9AJOIN\" >\u5927\u7684\u968f\u673a\u5206\u5e03\u8868\u548c\u5c0f\u7684\u968f\u673a\u5206\u5e03\u8868\u505aJOIN<\/a><ul class='ez-toc-list-level-4' ><li class='ez-toc-heading-level-4'><a class=\"ez-toc-link ez-toc-heading-44\" href=\"https:\/\/www.gbase8.cn\/en\/4100\/#LEFT_JOIN_%E5%B0%8F%E8%A1%A8%E6%8B%89%E5%A4%8D%E5%88%B6%E8%A1%A8\" >LEFT JOIN \u5c0f\u8868\u62c9\u590d\u5236\u8868<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-4'><a class=\"ez-toc-link ez-toc-heading-45\" href=\"https:\/\/www.gbase8.cn\/en\/4100\/#inner_join%E4%B9%9F%E6%98%AF%E5%B0%8F%E8%A1%A8%E6%8B%89%E5%A4%8D%E5%88%B6%E8%A1%A8\" >inner join\u4e5f\u662f\u5c0f\u8868\u62c9\u590d\u5236\u8868<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-4'><a class=\"ez-toc-link ez-toc-heading-46\" href=\"https:\/\/www.gbase8.cn\/en\/4100\/#right_join_%E5%A4%A7%E8%A1%A8%E6%8B%89%E4%BA%86%E5%A4%8D%E5%88%B6%E8%A1%A8\" >right join \u5927\u8868\u62c9\u4e86\u590d\u5236\u8868<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-4'><a class=\"ez-toc-link ez-toc-heading-47\" href=\"https:\/\/www.gbase8.cn\/en\/4100\/#right_join%E9%80%9A%E8%BF%87%E8%B0%83%E6%95%B4%E5%8F%82%E6%95%B0%EF%BC%8C%E5%A4%A7%E5%B0%8F%E8%A1%A8%E9%83%BD%E5%81%9A%E4%BA%86hash%E9%87%8D%E5%88%86%E5%B8%83\" >right join\u901a\u8fc7\u8c03\u6574\u53c2\u6570\uff0c\u5927\u5c0f\u8868\u90fd\u505a\u4e86hash\u91cd\u5206\u5e03<\/a><\/li><\/ul><\/li><\/ul><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-48\" href=\"https:\/\/www.gbase8.cn\/en\/4100\/#%E3%80%90%E9%AB%98%E3%80%91%E5%BD%93select%E5%88%97%E7%89%B9%E5%88%AB%E5%A4%9A%E6%97%B6%E7%9A%84%E5%B8%A6limit_%E7%9A%84%E6%8E%92%E5%BA%8F%E4%BC%98%E5%8C%96%E3%80%82\" >\u3010\u9ad8\u3011\u5f53select\u5217\u7279\u522b\u591a\u65f6\u7684\u5e26limit \u7684\u6392\u5e8f\u4f18\u5316\u3002<\/a><\/li><\/ul><\/nav><\/div>\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"%E5%8F%82%E8%80%83\"><\/span>\u53c2\u8003<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p>\u6267\u884c\u8ba1\u5212\u5404\u4e2a\u6b65\u9aa4\uff0c\u5404\u53c2\u6570\u7684\u542b\u4e49\uff0c\u8bf7\u53c2\u8003\u5982\u4e0b\u6587\u7ae0\u3002<\/p>\n\n\n\n<figure class=\"wp-block-embed is-type-wp-embed is-provider-\u8001\u7d2b\u7af9\u7684\u5bb6 wp-block-embed-\u8001\u7d2b\u7af9\u7684\u5bb6\"><div class=\"wp-block-embed__wrapper\">\n<blockquote class=\"wp-embedded-content\" data-secret=\"Rl58cjj8Mt\"><a href=\"https:\/\/www.gbase8.cn\/3600\">GBase 8a \u6267\u884c\u8ba1\u5212Explain\u4ecb\u7ecd<\/a><\/blockquote><iframe loading=\"lazy\" class=\"wp-embedded-content\" sandbox=\"allow-scripts\" security=\"restricted\" style=\"position: absolute; clip: rect(1px, 1px, 1px, 1px);\" title=\"\u300aGBase 8a \u6267\u884c\u8ba1\u5212Explain\u4ecb\u7ecd\u300b\u2014\u8001\u7d2b\u7af9\u7684\u5bb6\" src=\"https:\/\/www.gbase8.cn\/3600\/embed#?secret=Rl58cjj8Mt\" data-secret=\"Rl58cjj8Mt\" width=\"600\" height=\"338\" frameborder=\"0\" marginwidth=\"0\" marginheight=\"0\" scrolling=\"no\"><\/iframe>\n<\/div><\/figure>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"%E7%8E%AF%E5%A2%83\"><\/span>\u73af\u5883<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<h3 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"%E8%8A%82%E7%82%B9%E6%95%B0\"><\/span>\u8282\u70b9\u6570<span class=\"ez-toc-section-end\"><\/span><\/h3>\n\n\n\n<p>2\u8282\u70b9\u96c6\u7fa4\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>&#91;root@rh6-1 ~]# gcadmin\nCLUSTER STATE:  ACTIVE\nCLUSTER MODE:   NORMAL\n\n=================================================================\n|             GBASE COORDINATOR CLUSTER INFORMATION             |\n=================================================================\n|   NodeName   |     IpAddress     |gcware |gcluster |DataState |\n-----------------------------------------------------------------\n| coordinator1 |    10.0.2.201     | OPEN  |  OPEN   |    0     |\n-----------------------------------------------------------------\n=============================================================\n|              GBASE DATA CLUSTER INFORMATION               |\n=============================================================\n|NodeName |     IpAddress     |gnode |syncserver |DataState |\n-------------------------------------------------------------\n|  node1  |    10.0.2.201     | OPEN |   OPEN    |    0     |\n-------------------------------------------------------------\n|  node2  |    10.0.2.202     | OPEN |   OPEN    |    0     |\n-------------------------------------------------------------\n<\/code><\/pre>\n\n\n\n<h3 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"%E9%9B%86%E7%BE%A4%E7%89%88%E6%9C%AC\"><\/span>\u96c6\u7fa4\u7248\u672c<span class=\"ez-toc-section-end\"><\/span><\/h3>\n\n\n\n<p>8.6.2.43<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>&#91;gbase@rh6-1 ~]$ gccli -e\"select version()\"\n+----------------------+\n| version()            |\n+----------------------+\n| 8.6.2.43-R28 .125499 |\n+----------------------+\n<\/code><\/pre>\n\n\n\n<h3 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"%E6%95%B0%E6%8D%AE\"><\/span>\u6570\u636e<span class=\"ez-toc-section-end\"><\/span><\/h3>\n\n\n\n<h4 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"%E9%9A%8F%E6%9C%BA%E5%88%86%E5%B8%83%E8%A1%A8T1%E5%92%8Ct1_2\"><\/span>\u968f\u673a\u5206\u5e03\u8868T1\u548ct1_2<span class=\"ez-toc-section-end\"><\/span><\/h4>\n\n\n\n<p>\u6ce8\u610f\u5176\u6570\u636e\u91cf\u5dee\u8ddd\uff0ct1\u662f3300\u4e07\u884c\uff0ct1_2\u662f1000\u884c\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>CREATE TABLE \"t1\" (\n  \"id\" int(11) DEFAULT NULL,\n  \"name\" varchar(100) DEFAULT NULL\n) ENGINE=EXPRESS \n\ngbase> create table t1_2 like t1;\r\nQuery OK, 0 rows affected (Elapsed: 00:00:00.65)\r\n\ngbase> select count(*) from t1;\r\n+----------+\r\n| count(*) |\r\n+----------+\r\n| 33000001 |\r\n+----------+\r\n1 row in set (Elapsed: 00:00:00.50)\r\n\r\ngbase> select count(*) from t1_2;\r\n+----------+\r\n| count(*) |\r\n+----------+\r\n|     1000 |\r\n+----------+\r\n1 row in set (Elapsed: 00:00:00.68)\r\n<\/code><\/pre>\n\n\n\n<h4 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Hash%E5%88%86%E5%B8%83%E8%A1%A8td_Distribution\"><\/span>Hash\u5206\u5e03\u8868td (Distribution)<span class=\"ez-toc-section-end\"><\/span><\/h4>\n\n\n\n<pre class=\"wp-block-code\"><code> CREATE TABLE \"td\" (\n  \"id\" int(11) DEFAULT NULL,\n  \"name\" varchar(100) DEFAULT NULL\n) ENGINE=EXPRESS DISTRIBUTED BY('id')\n\ngbase> create table td_2 like td;\nQuery OK, 0 rows affected (Elapsed: 00:00:00.49)\n\ngbase> select count(*) from td;\r\n+----------+\r\n| count(*) |\r\n+----------+\r\n| 33000001 |\r\n+----------+\r\n1 row in set (Elapsed: 00:00:00.16)\r\n\r\ngbase> select count(*) from td_2;\r\n+----------+\r\n| count(*) |\r\n+----------+\r\n|     1000 |\r\n+----------+\r\n1 row in set (Elapsed: 00:00:01.03)\r\n\r\n<\/code><\/pre>\n\n\n\n<h4 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Hash%E5%88%86%E5%B8%83%E8%A1%A8td_name%E5%88%86%E5%B8%83%E5%88%97%E4%B8%8D%E5%90%8C%EF%BC%89\"><\/span>Hash\u5206\u5e03\u8868td_name(\u5206\u5e03\u5217\u4e0d\u540c\uff09<span class=\"ez-toc-section-end\"><\/span><\/h4>\n\n\n\n<pre class=\"wp-block-code\"><code>CREATE TABLE \"td_name\" (\r\n  \"id\" int(11) DEFAULT NULL,\r\n  \"name\" varchar(100) DEFAULT NULL\r\n) ENGINE=EXPRESS DISTRIBUTED BY('name') \n\ngbase> select count(*) from td_name;\r\n+----------+\r\n| count(*) |\r\n+----------+\r\n| 33000001 |\r\n+----------+\r\n1 row in set (Elapsed: 00:00:00.14)\r\n<\/code><\/pre>\n\n\n\n<h4 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"%E5%A4%8D%E5%88%B6%E8%A1%A8tr_Replicated\"><\/span>\u590d\u5236\u8868tr (Replicated)<span class=\"ez-toc-section-end\"><\/span><\/h4>\n\n\n\n<pre class=\"wp-block-code\"><code> CREATE TABLE \"tr\" (\n  \"id\" int(11) DEFAULT NULL,\n  \"name\" varchar(100) DEFAULT NULL\n) ENGINE=EXPRESS REPLICATED<\/code><\/pre>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"%E3%80%90%E5%88%9D%E3%80%91%E5%8D%95%E8%A1%A8count\"><\/span>\u3010\u521d\u3011\u5355\u8868count(*)<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p>\u76ee\u524d\u4e0d\u663e\u793a\u4efb\u4f55\u4efb\u4f55\u7ec6\u8282\uff0c\u5185\u90e8\u5c31\u662f\u5404\u4e2a\u8282\u70b9\u81ea\u5df1count(*),\u7136\u540e\u5c06\u884c\u6570\u52a0\u5728\u4e00\u8d77\u8fd4\u56de\u5373\u53ef\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>gbase&gt; explain select count(*) from t1;\n+------------------+\n| QueryPlan        |\n+------------------+\n| Count optimized. |\n+------------------+\n1 row in set (Elapsed: 00:00:00.01)\n\ngbase&gt; explain select count(*) from t1 where id&gt;10;\n+------------------+\n| QueryPlan        |\n+------------------+\n| Count optimized. |\n+------------------+\n1 row in set (Elapsed: 00:00:00.01)\n<\/code><\/pre>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"%E3%80%90%E5%88%9D%E3%80%91%E5%8D%95%E8%A1%A8%E7%AE%80%E5%8D%95%E6%9F%A5%E8%AF%A2\"><\/span>\u3010\u521d\u3011\u5355\u8868\u7b80\u5355\u67e5\u8be2<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<h3 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"%E6%97%A0%E8%BF%87%E6%BB%A4%E6%9D%A1%E4%BB%B6\"><\/span>\u65e0\u8fc7\u6ee4\u6761\u4ef6<span class=\"ez-toc-section-end\"><\/span><\/h3>\n\n\n\n<p>\u4ece\u5982\u4e0b\u6267\u884c\u8ba1\u5212\u770b\u53ea\u67091\u6b65\uff1a<\/p>\n\n\n\n<ul class=\"wp-block-list\"><li>MOTION\uff1aRESULT \u5c06\u7ed3\u679c\u53d1\u9001\u7ed9\u8c03\u7528\u7aef<\/li><li>OPERATION\uff1aTABLE,\u4ee3\u8868\u65e0\u4efb\u4f55\u6761\u4ef6\u7684\u5355\u8868\u64cd\u4f5c\u3002<\/li><li>TABLE\uff1aT1[DIS]\uff0c\u6d89\u53ca\u5230\u7684\u8868\u662fT1, DIS\u8868\u793a\u968f\u673a\u5206\u5e03<\/li><li>CONDITION\uff1a\u7a7a<\/li><\/ul>\n\n\n\n<pre class=\"wp-block-code\"><code>gbase&gt; explain select * from t1;\n+----+----------+-----------+---------+-----------+-----------------+\n| ID | MOTION   | OPERATION | TABLE   | CONDITION | NO STAT Tab\/Col |\n+----+----------+-----------+---------+-----------+-----------------+\n| 00 | &#91;RESULT] |  Table    | t1&#91;DIS] |           | t1              |\n+----+----------+-----------+---------+-----------+-----------------+\n1 row in set (Elapsed: 00:00:00.00)\n<\/code><\/pre>\n\n\n\n<p>Hash\u5206\u5e03\u8868\u7684TABLE\u663e\u793a\u4e3a\u5206\u5e03\u5217[id]<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>gbase&gt; explain select * from td;\n+----+----------+-----------+--------+-----------+-----------------+\n| ID | MOTION   | OPERATION | TABLE  | CONDITION | NO STAT Tab\/Col |\n+----+----------+-----------+--------+-----------+-----------------+\n| 00 | &#91;RESULT] |  Table    | td&#91;id] |           | td              |\n+----+----------+-----------+--------+-----------+-----------------+\n1 row in set (Elapsed: 00:00:00.00)\n<\/code><\/pre>\n\n\n\n<p>\u590d\u5236\u8868\u7684TABLE\u663e\u793a\u4e3a[REP]<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>gbase&gt; explain select * from tr;\n+----+----------+-----------+---------+-----------+-----------------+\n| ID | MOTION   | OPERATION | TABLE   | CONDITION | NO STAT Tab\/Col |\n+----+----------+-----------+---------+-----------+-----------------+\n| 00 | &#91;RESULT] |  Table    | tr&#91;REP] |           | tr              |\n+----+----------+-----------+---------+-----------+-----------------+\n1 row in set (Elapsed: 00:00:00.01)\n<\/code><\/pre>\n\n\n\n<h3 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"%E5%B8%A6%E5%8D%95%E4%B8%AA%E8%BF%87%E6%BB%A4%E6%9D%A1%E4%BB%B6\"><\/span>\u5e26\u5355\u4e2a\u8fc7\u6ee4\u6761\u4ef6<span class=\"ez-toc-section-end\"><\/span><\/h3>\n\n\n\n<p>\u53ea\u67091\u6b65\u3002<\/p>\n\n\n\n<ul class=\"wp-block-list\" id=\"block-a13c7cdb-489b-4c61-b631-c4f659717471\"><li>MOTION\uff1aRESULT \u5c06\u7ed3\u679c\u53d1\u9001\u7ed9\u8c03\u7528\u7aef<\/li><li>OPERATION\uff1aSCAN ,\u5355\u8868\u626b\u63cf\uff0c\u5e76\u4f7f\u7528\u6761\u4ef6\u8fc7\u6ee4\u6570\u636e\u3002<\/li><li>TABLE\uff1aT1[DIS]\uff0c\u6d89\u53ca\u5230\u7684\u8868\u662fT1,\u5206\u5e03\u8868<\/li><li>CONDITION\uff1aid{S} &gt; 10\uff0c\u9488\u5bf9SCAN\uff0c\u4e3a\u626b\u63cf\u6761\u4ef6 id&gt;10<\/li><\/ul>\n\n\n\n<pre class=\"wp-block-code\"><code>gbase&gt; explain select * from t1 where id&gt;10;\n+----+----------+-----------+---------+--------------+-----------------+\n| ID | MOTION   | OPERATION | TABLE   | CONDITION    | NO STAT Tab\/Col |\n+----+----------+-----------+---------+--------------+-----------------+\n| 00 | &#91;RESULT] |  SCAN     | t1&#91;DIS] | (id{S} &gt; 10) | t1              |\n+----+----------+-----------+---------+--------------+-----------------+\n1 row in set (Elapsed: 00:00:00.00)\n<\/code><\/pre>\n\n\n\n<p>Hash\u5206\u5e03\u8868\u548c\u590d\u5236\u8868\u7684\u57fa\u672c\u76f8\u540c\uff0c\u53ea\u662f\u6d89\u53ca\u7684TABLE\u5217\u4e0d\u4e00\u6837\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>gbase&gt; explain select * from td where id&gt;10;\n+----+----------+-----------+--------+--------------+-----------------+\n| ID | MOTION   | OPERATION | TABLE  | CONDITION    | NO STAT Tab\/Col |\n+----+----------+-----------+--------+--------------+-----------------+\n| 00 | &#91;RESULT] |  SCAN     | td&#91;id] | (id{S} &gt; 10) | td              |\n+----+----------+-----------+--------+--------------+-----------------+\n1 row in set (Elapsed: 00:00:00.00)\n\ngbase&gt; explain select * from tr where id&gt;10;\n+----+----------+-----------+---------+--------------+-----------------+\n| ID | MOTION   | OPERATION | TABLE   | CONDITION    | NO STAT Tab\/Col |\n+----+----------+-----------+---------+--------------+-----------------+\n| 00 | &#91;RESULT] |  SCAN     | tr&#91;REP] | (id{S} &gt; 10) | tr              |\n+----+----------+-----------+---------+--------------+-----------------+\n1 row in set (Elapsed: 00:00:00.00)\n<\/code><\/pre>\n\n\n\n<h3 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"%E5%B8%A6%E5%A4%9A%E4%B8%AA%E8%BF%87%E6%BB%A4%E6%9D%A1%E4%BB%B6\"><\/span>\u5e26\u591a\u4e2a\u8fc7\u6ee4\u6761\u4ef6<span class=\"ez-toc-section-end\"><\/span><\/h3>\n\n\n\n<p>\u6267\u884c\u8ba1\u5212\u548c\u5355\u4e2a\u6761\u4ef6\u7684\u57fa\u672c\u4e00\u81f4\uff0c\u533a\u522b\u5c31\u662fCONDITION\u6761\u4ef6\u5217\u53d8\u6210\u4e86\u591a\u4e2a\uff0c\u91c7\u7528\u591a\u884c\u7684\u5f62\u5f0f\u663e\u793a\u3002<\/p>\n\n\n\n<p>\u6ce8\u610f\u5176\u4e2d\u7684\u6570\u5b57\u7c7b\u578b\uff0c\u88ab\u5185\u90e8\u5f3a\u5236\u8f6c\u6362\u6210char\u7c7b\u578b\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>gbase&gt; explain select * from t1 where id&gt;10 and id&lt;100 and id like '%3%';\n+----+----------+-----------+---------+-----------------------------------+-----------------+\n| ID | MOTION   | OPERATION | TABLE   | CONDITION                         | NO STAT Tab\/Col |\n+----+----------+-----------+---------+-----------------------------------+-----------------+\n| 00 | &#91;RESULT] |  SCAN     | t1&#91;DIS] | (id{S} &gt; 10)                      | t1              |\n|    |          |           |         | (id{S} &lt; 100)                     |                 |\n|    |          |           |         | (cast(id as char(11)) LIKE '%3%') |                 |\n+----+----------+-----------+---------+-----------------------------------+-----------------+\n3 rows in set (Elapsed: 00:00:00.00)\n\ngbase&gt; explain select * from td where id&gt;10 and id&lt;100 and id like '%3%';\n+----+----------+-----------+--------+-----------------------------------+-----------------+\n| ID | MOTION   | OPERATION | TABLE  | CONDITION                         | NO STAT Tab\/Col |\n+----+----------+-----------+--------+-----------------------------------+-----------------+\n| 00 | &#91;RESULT] |  SCAN     | td&#91;id] | (id{S} &gt; 10)                      | td              |\n|    |          |           |        | (id{S} &lt; 100)                     |                 |\n|    |          |           |        | (cast(id as char(11)) LIKE '%3%') |                 |\n+----+----------+-----------+--------+-----------------------------------+-----------------+\n3 rows in set (Elapsed: 00:00:00.01)\n\ngbase&gt; explain select * from tr where id&gt;10 and id&lt;100 and id like '%3%';\n+----+----------+-----------+---------+-----------------------------------+-----------------+\n| ID | MOTION   | OPERATION | TABLE   | CONDITION                         | NO STAT Tab\/Col |\n+----+----------+-----------+---------+-----------------------------------+-----------------+\n| 00 | &#91;RESULT] |  SCAN     | tr&#91;REP] | (id{S} &gt; 10)                      | tr              |\n|    |          |           |         | (id{S} &lt; 100)                     |                 |\n|    |          |           |         | (cast(id as char(11)) LIKE '%3%') |                 |\n+----+----------+-----------+---------+-----------------------------------+-----------------+\n3 rows in set (Elapsed: 00:00:00.00)\n\n<\/code><\/pre>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"%E3%80%90%E5%88%9D%E3%80%91%E5%8D%95%E8%A1%A8%E5%85%A8%E6%8E%92%E5%BA%8F\"><\/span>\u3010\u521d\u3011\u5355\u8868\u5168\u6392\u5e8f<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p>\u5168\u6392\u5e8f\u5bf9\u968f\u673a\u5206\u5e03\u8868\u548cHash\u5206\u5e03\u8868\u6ca1\u6709\u533a\u522b\uff0c\u90fd\u9700\u8981\u5148\u62c9\u5230\u4e00\u4e2a\u8282\u70b9\u540e\uff0c\u518d\u8fdb\u884c\u3002\u6267\u884c\u8ba1\u5212\u5206\u6210\u4e862\u6b65\uff1a\u5148\u4ece\u5404\u4e2a\u8282\u70b9\u5c06\u6570\u636e\u53d1\u9001\u5230\u6c47\u603b\u8282\u70b9\u7684\u8868\u91cc\uff1b\u7136\u540e\u5728\u6c47\u603b\u8868\u91cc\uff0c\u6839\u636e\u6761\u4ef6\u6392\u5e8f\u540e\uff0c\u8fd4\u56de\u3002<\/p>\n\n\n\n<p>\u7b2c00\u6b65\u3002<\/p>\n\n\n\n<ul class=\"wp-block-list\" id=\"block-c74e3470-d996-4d47-8b07-c9c379bf435a\"><li>MOTION\uff1aGATHER \u7ed3\u679c\u53d1\u7ed9\u6c47\u603b\u8282\u70b9<\/li><li>OPERATION\uff1aTABLE \u5168\u8868\u3002<\/li><li>TABLE\uff1aT1[DIS]\uff0cT1\u8868\u662f\u5206\u5e03\u8868\uff0c td[id], td\u8868\u662fHash\u5206\u5e03\u8868\u3002<\/li><li>CONDITION\uff1a\u7a7a<\/li><\/ul>\n\n\n\n<p>\u7b2c01\u6b65<\/p>\n\n\n\n<ul class=\"wp-block-list\" id=\"block-0436962f-89d3-471d-b1cb-3e808fb6175a\"><li>MOTION\uff1aRESULT \u7ed3\u679c\u53d1\u7ed9\u8c03\u7528\u65b9\u5ba2\u6237\u7aef<\/li><li>OPERATION\uff1aStep \u4f7f\u7528\u524d\u4e00\u6b65\u7684\u7ed3\u679c\u3002 Order \u6392\u5e8f\u64cd\u4f5c\u3002<\/li><li>TABLE\uff1aT1[DIS]\uff0c00 \u7b2c\u4e00\u6b65\u6c47\u603b\u8282\u70b9\u7684\u8868<\/li><li>CONDITION\uff1a\u5bf9Order\u6392\u5e8f\uff0c\u6307\u6392\u5e8f\u7684\u6761\u4ef6<\/li><\/ul>\n\n\n\n<pre class=\"wp-block-code\"><code>gbase&gt; explain select * from t1 order by id ;\n+----+----------+-----------+---------+-----------------+-----------------+\n| ID | MOTION   | OPERATION | TABLE   | CONDITION       | NO STAT Tab\/Col |\n+----+----------+-----------+---------+-----------------+-----------------+\n| 01 | &#91;RESULT] |  Step     | &lt;00&gt;    |                 |                 |\n|    |          |  ORDER    |         | ORDER BY id ASC |                 |\n| 00 | &#91;GATHER] |  Table    | t1&#91;DIS] |                 | t1              |\n+----+----------+-----------+---------+-----------------+-----------------+\n3 rows in set (Elapsed: 00:00:00.01)\n\ngbase&gt;\ngbase&gt; explain select * from td order by id ;\n+----+----------+-----------+--------+-----------------+-----------------+\n| ID | MOTION   | OPERATION | TABLE  | CONDITION       | NO STAT Tab\/Col |\n+----+----------+-----------+--------+-----------------+-----------------+\n| 01 | &#91;RESULT] |  Step     | &lt;00&gt;   |                 |                 |\n|    |          |  ORDER    |        | ORDER BY id ASC |                 |\n| 00 | &#91;GATHER] |  Table    | td&#91;id] |                 | td              |\n+----+----------+-----------+--------+-----------------+-----------------+\n3 rows in set (Elapsed: 00:00:00.01)\n<\/code><\/pre>\n\n\n\n<p>\u5bf9\u590d\u5236\u8868\uff0c\u56e0\u4e3a\u6bcf\u4e2a\u8282\u70b9\u6570\u636e\u90fd\u662f\u4e00\u6837\u7684\uff0c\u6240\u4ee5\u4e0d\u9700\u8981\u6c47\u603b\u8fd9\u4e00\u6b65\uff0c\u76f4\u63a5\u505a\u6392\u5e8f\u8fd4\u56de\u5373\u53ef\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>gbase&gt; explain select * from tr order by id ;\n+----+----------+-----------+---------+-----------------+-----------------+\n| ID | MOTION   | OPERATION | TABLE   | CONDITION       | NO STAT Tab\/Col |\n+----+----------+-----------+---------+-----------------+-----------------+\n| 00 | &#91;RESULT] |  Table    | tr&#91;REP] |                 | tr              |\n|    |          |  ORDER    |         | ORDER BY id ASC |                 |\n+----+----------+-----------+---------+-----------------+-----------------+\n2 rows in set (Elapsed: 00:00:00.01)\n<\/code><\/pre>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"%E3%80%90%E5%88%9D%E3%80%91%E5%8D%95%E8%A1%A8%E5%B8%A6limit%E6%8E%92%E5%BA%8F\"><\/span>\u3010\u521d\u3011\u5355\u8868\u5e26limit\u6392\u5e8f<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p>\u5e26limit\u7684\u6392\u5e8f\uff0c\u5728GBase\u6570\u636e\u5e93\u91cc\u9762\uff0c\u91c7\u7528\u7684\u662f\u5728\u6bcf\u4e2a\u8282\u70b9\u5148\u6392\u5e8f\u5e76\u8fd4\u56delimit\u7684\u7ed3\u679c\u96c6\u5230\u6c47\u603b\u8868\uff0c\u7136\u540e\u6c47\u603b\u8868\u518d\u6b21\u505a\u4e00\u6b21order\u8fd4\u56de\u6700\u7ec8\u7ed3\u679c\uff0c\u540c\u6837\u662f2\u6b65\uff1a<\/p>\n\n\n\n<p>\u7b2c00\u6b65\u3002<\/p>\n\n\n\n<ul class=\"wp-block-list\" id=\"block-c74e3470-d996-4d47-8b07-c9c379bf435a\"><li>MOTION\uff1aGATHER \u7ed3\u679c\u53d1\u7ed9\u6c47\u603b\u8282\u70b9<\/li><li>OPERATION\uff1aTABLE \u5168\u8868\uff1bOrder \u6392\u5e8f\uff1b limit \u8fd4\u56de\u6709\u9650\u7ed3\u679c\u96c6<\/li><li>TABLE\uff1aT1[DIS]\uff0cT1\u8868\u662f\u5206\u5e03\u8868\uff0c td[id], td\u8868\u662fHash\u5206\u5e03\u8868\u3002<\/li><li>CONDITION\uff1a\u5bf9Order\u662f\u6392\u5e8f\u7684\u6761\u4ef6\uff1b LIMIT\u662f\u7ed3\u679c\u96c6\u884c\u6570<\/li><\/ul>\n\n\n\n<p>\u7b2c01\u6b65<\/p>\n\n\n\n<ul class=\"wp-block-list\" id=\"block-0436962f-89d3-471d-b1cb-3e808fb6175a\"><li>MOTION\uff1aRESULT \u7ed3\u679c\u53d1\u7ed9\u8c03\u7528\u65b9\u5ba2\u6237\u7aef<\/li><li>OPERATION\uff1aStep \u4f7f\u7528\u524d\u4e00\u6b65\u7684\u7ed3\u679c\u3002 Order \u6392\u5e8f\uff1b limit \u8fd4\u56de\u6709\u9650\u7ed3\u679c\u96c6<\/li><li>TABLE\uff1aT1[DIS]\uff0c00 \u7b2c\u4e00\u6b65\u6c47\u603b\u8282\u70b9\u7684\u8868<\/li><li>CONDITION\uff1a\u5bf9Order\u6392\u5e8f\uff0c\u6307\u6392\u5e8f\u7684\u6761\u4ef6\uff1bLIMIT\u662f\u7ed3\u679c\u96c6\u884c\u6570<\/li><\/ul>\n\n\n\n<pre class=\"wp-block-code\"><code>gbase&gt; explain select * from t1 order by id  limit 1;\n+----+----------+-----------+---------+-----------------+-----------------+\n| ID | MOTION   | OPERATION | TABLE   | CONDITION       | NO STAT Tab\/Col |\n+----+----------+-----------+---------+-----------------+-----------------+\n| 01 | &#91;RESULT] |  Step     | &lt;00&gt;    |                 |                 |\n|    |          |  ORDER    |         | ORDER BY id ASC |                 |\n|    |          |  LIMIT    |         | LIMIT 1         |                 |\n| 00 | &#91;GATHER] |  Table    | t1&#91;DIS] |                 | t1              |\n|    |          |  ORDER    |         | ORDER BY id ASC |                 |\n|    |          |  LIMIT    |         | LIMIT 1         |                 |\n+----+----------+-----------+---------+-----------------+-----------------+\n6 rows in set (Elapsed: 00:00:00.00)\n\ngbase&gt; explain select * from td order by id  limit 1;\n+----+----------+-----------+--------+-----------------+-----------------+\n| ID | MOTION   | OPERATION | TABLE  | CONDITION       | NO STAT Tab\/Col |\n+----+----------+-----------+--------+-----------------+-----------------+\n| 01 | &#91;RESULT] |  Step     | &lt;00&gt;   |                 |                 |\n|    |          |  ORDER    |        | ORDER BY id ASC |                 |\n|    |          |  LIMIT    |        | LIMIT 1         |                 |\n| 00 | &#91;GATHER] |  Table    | td&#91;id] |                 | td              |\n|    |          |  ORDER    |        | ORDER BY id ASC |                 |\n|    |          |  LIMIT    |        | LIMIT 1         |                 |\n+----+----------+-----------+--------+-----------------+-----------------+\n6 rows in set (Elapsed: 00:00:00.00)\n<\/code><\/pre>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"%E3%80%90%E5%88%9D%E3%80%91%E5%8D%95%E8%A1%A8%E5%85%A8%E9%83%A8%E8%81%9A%E5%90%88GROUP\"><\/span>\u3010\u521d\u3011\u5355\u8868\u5168\u90e8\u805a\u5408GROUP<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<h3 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"%E9%9A%8F%E6%9C%BA%E5%88%86%E5%B8%83%E8%A1%A8\"><\/span>\u968f\u673a\u5206\u5e03\u8868<span class=\"ez-toc-section-end\"><\/span><\/h3>\n\n\n\n<p>\u90fd\u662f\u5148\u505a\u91cd\u5206\u5e03[REDIST]\u5230\u4e34\u65f6\u8868,\u7136\u540e\u5728\u4e34\u65f6\u8868\u91cc\u505a\u505a\u72d7\u7684group\u64cd\u4f5c\u5e76\u8fd4\u56de\u3002<\/p>\n\n\n\n<ul class=\"wp-block-list\"><li>00\uff1a\u6839\u636eid\u5217\u8fdb\u884c\u672c\u5730GROUP\u805a\u5408\u540e\uff0c\u5c06\u7ed3\u679cREDIST\u91cd\u5206\u5e03\u5230\u4e34\u65f6\u8868<\/li><li>01\uff1a\u91c7\u752800\u6b65\u7684\u4e34\u65f6\u8868\uff0c\u8fdb\u884c\u4e8c\u6b21GROUP\u805a\u5408\uff0c\u5e76\u8fd4\u56de\u7ed3\u679c[RESULT}<\/li><\/ul>\n\n\n\n<pre class=\"wp-block-code\"><code>gbase&gt; explain select id,count(*) from t1 group by id;\n+----+--------------+-----------+---------+-------------+-----------------+\n| ID | MOTION       | OPERATION | TABLE   | CONDITION   | NO STAT Tab\/Col |\n+----+--------------+-----------+---------+-------------+-----------------+\n| 01 | &#91;RESULT]     |  Step     | &lt;00&gt;    |             |                 |\n|    |              |  GROUP    |         | GROUP BY id |                 |\n| 00 | &#91;REDIST(id)] |  Table    | t1&#91;DIS] |             | t1              |\n|    |              |  GROUP    |         | GROUP BY id |                 |\n+----+--------------+-----------+---------+-------------+-----------------+\n4 rows in set (Elapsed: 00:00:00.00)\n<\/code><\/pre>\n\n\n\n<h3 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Hash%E5%88%86%E5%B8%83%E8%A1%A8\"><\/span>Hash\u5206\u5e03\u8868<span class=\"ez-toc-section-end\"><\/span><\/h3>\n\n\n\n<h4 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"%E8%81%9A%E5%90%88%E5%88%97%E4%B8%8D%E6%98%AF%E5%88%86%E5%B8%83%E5%88%97\"><\/span>\u805a\u5408\u5217\u4e0d\u662f\u5206\u5e03\u5217<span class=\"ez-toc-section-end\"><\/span><\/h4>\n\n\n\n<p>\u6267\u884c\u8ba1\u5212\u548c\u968f\u673a\u5206\u5e03\u8868\u662f\u4e00\u6837\u7684\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>gbase&gt; explain select name,count(*) from td group by name;\n+----+----------------+-----------+--------+---------------+-----------------+\n| ID | MOTION         | OPERATION | TABLE  | CONDITION     | NO STAT Tab\/Col |\n+----+----------------+-----------+--------+---------------+-----------------+\n| 01 | &#91;RESULT]       |  Step     | &lt;00&gt;   |               |                 |\n|    |                |  GROUP    |        | GROUP BY name |                 |\n| 00 | &#91;REDIST(name)] |  Table    | td&#91;id] |               | td              |\n|    |                |  GROUP    |        | GROUP BY name |                 |\n+----+----------------+-----------+--------+---------------+-----------------+\n4 rows in set (Elapsed: 00:00:00.01)\n<\/code><\/pre>\n\n\n\n<h4 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"%E8%81%9A%E5%90%88%E5%88%97%E5%8C%85%E5%90%AB%E5%88%86%E5%B8%83%E5%88%97\"><\/span>\u805a\u5408\u5217\u5305\u542b\u5206\u5e03\u5217<span class=\"ez-toc-section-end\"><\/span><\/h4>\n\n\n\n<p>\u53ef\u4ee5\u770b\u5230\uff0c\u56e0\u4e3a\u805a\u5408\u5217\u5305\u542b\u4e86Hash\u5206\u5e03\u5217\uff0c\u548c\u5206\u5e03\u5217\u6709\u5173\u7684\u6570\u636e\u90fd\u5728\u540c\u4e00\u4e2a\u8282\u70b9\u4e0a\uff0c\u5404\u4e2a\u8282\u70b9\u5404\u81ea\u505agroup\uff0c\u7136\u540e\u8fd4\u56de\u7ed3\u679c\u5c31\u53ef\u4ee5\u4e86\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>gbase&gt; explain select id,count(*) from td group by id;\n+----+----------+-----------+--------+-------------+-----------------+\n| ID | MOTION   | OPERATION | TABLE  | CONDITION   | NO STAT Tab\/Col |\n+----+----------+-----------+--------+-------------+-----------------+\n| 00 | &#91;RESULT] |  Table    | td&#91;id] |             | td              |\n|    |          |  GROUP    |        | GROUP BY id |                 |\n+----+----------+-----------+--------+-------------+-----------------+\n2 rows in set (Elapsed: 00:00:00.01)\n<\/code><\/pre>\n\n\n\n<h3 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"%E5%A4%8D%E5%88%B6%E8%A1%A8\"><\/span>\u590d\u5236\u8868<span class=\"ez-toc-section-end\"><\/span><\/h3>\n\n\n\n<p>\u4e0e\u805a\u5408\u5217\u5305\u542bHash\u5206\u5e03\u8868\u7684\u5206\u5e03\u5217\u4e00\u6837\uff0c\u90fd\u662f\u4e00\u6b65\u51fa\u7ed3\u679c\uff0c\u4e0d\u9700\u8981\u8282\u70b9\u95f4\u62c9\u6570\u636e\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>gbase&gt; explain select id,count(*) from tr group by id;\n+----+----------+-----------+---------+-------------+-----------------+\n| ID | MOTION   | OPERATION | TABLE   | CONDITION   | NO STAT Tab\/Col |\n+----+----------+-----------+---------+-------------+-----------------+\n| 00 | &#91;RESULT] |  Table    | tr&#91;REP] |             | tr              |\n|    |          |  GROUP    |         | GROUP BY id |                 |\n+----+----------+-----------+---------+-------------+-----------------+\n2 rows in set (Elapsed: 00:00:00.00)\n<\/code><\/pre>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"%E3%80%90%E4%B8%AD%E3%80%91TOPN%E5%B8%A6%E6%8E%92%E5%BA%8F%E5%92%8C%E6%9C%89%E9%99%90%E7%BB%93%E6%9E%9C%E7%9A%84%E7%9A%84%E8%81%9A%E5%90%88\"><\/span>\u3010\u4e2d\u3011TOPN\u5e26\u6392\u5e8f\u548c\u6709\u9650\u7ed3\u679c\u7684\u7684\u805a\u5408<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p>\u8fd9\u4e2a\u573a\u666f\u6570\u636e\u6700\u5e38\u89c1\u7684TOPN\u573a\u666f\uff0c\u6309\u7167\u805a\u5408\u7684\u6570\u636e\u6392\u5e8f\uff0c\u5e76\u8fd4\u56de\u6709\u9650\u7684\u90e8\u5206\u6570\u636e\uff0c\u6bd4\u5982\u4eba\u6570\u6700\u591a\u7684\u7701\u4efd\u524d10\u540d\u3002<\/p>\n\n\n\n<h3 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"%E9%9A%8F%E6%9C%BA%E5%88%86%E5%B8%83%E8%A1%A8-2\"><\/span>\u968f\u673a\u5206\u5e03\u8868<span class=\"ez-toc-section-end\"><\/span><\/h3>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"894\" height=\"239\" src=\"https:\/\/www.gbase8.cn\/wp-content\/uploads\/2021\/02\/image.png\" alt=\"GBase 8a\u6267\u884c\u8ba1\u5212 explain TOPN\u5e26\u6392\u5e8f\u548c\u6709\u9650\u7ed3\u679c\u7684\u7684\u805a\u5408\" class=\"wp-image-4167\"\/><figcaption>GBase 8a \u6267\u884c\u8ba1\u5212 explain TOPN\u5e26\u6392\u5e8f\u548c\u6709\u9650\u7ed3\u679c\u7684\u7684\u805a\u5408<\/figcaption><\/figure>\n\n\n\n<p>\u9996\u5148\u8fd8\u662f\u8981\u6309\u7167\u805a\u5408\u5217\u505a\u91cd\u5206\u5e03\uff0c\u7136\u540e\u518d\u505a\u5404\u81ea\u7684\u6709\u9650\u7ed3\u679c\u96c6\u7684\u6392\u5e8f\uff0c\u5e76\u6c47\u603b\u5230\u4e00\u4e2a\u8282\u70b9\uff0c\u6700\u540e\u505a\u4e8c\u6b21\u6709\u9650\u7ed3\u679c\u96c6\u7684\u6392\u5e8f\u5e76\u8fd4\u56de\u7ed3\u679c\u3002<\/p>\n\n\n\n<ul class=\"wp-block-list\"><li>00\uff1a\u6309\u7167\u805a\u5408\u5217id\uff0c\u672c\u5730\u805a\u5408\u540e\uff0c\u8fdb\u884c\u91cd\u5206\u5e03(REDIST)<\/li><li>01\uff1a\u4f7f\u752800\u6b65\u9aa4\u7684\u8868\uff0c\u505a\u672c\u5730\u7684\u6709\u9650\u7ed3\u679c\u96c6\u7684\u6392\u5e8f(order limit)\uff0c\u7ed3\u679c\u653e\u5230\u6c47\u603b\u8868[GATHER]<\/li><li>02\uff1a\u4f7f\u752801\u7684\u6c47\u603b\u8868\uff0c\u505a\u7b2c\u4e8c\u6b21\u6709\u9650\u7ed3\u679c\u96c6\u7684\u6392\u5e8f(order limit)\uff0c\u5e76\u8fd4\u56de\u7ed3\u679c\u5230\u8c03\u7528\u7aef[RESULT]<\/li><\/ul>\n\n\n\n<pre class=\"wp-block-code\"><code>gbase&gt; explain select id,count(*) from t1 group by id order by count(*) desc limit 10;\n+----+--------------+-----------+---------+-------------------------------------------------+-----------------+\n| ID | MOTION       | OPERATION | TABLE   | CONDITION                                       | NO STAT Tab\/Col |\n+----+--------------+-----------+---------+-------------------------------------------------+-----------------+\n| 02 | &#91;RESULT]     |  Step     | &lt;01&gt;    |                                                 |                 |\n|    |              |  ORDER    |         | ORDER BY cast(SUM_2ND(COUNT(0)) as signed) DESC |                 |\n|    |              |  LIMIT    |         | LIMIT 10                                        |                 |\n| 01 | &#91;GATHER]     |  Step     | &lt;00&gt;    |                                                 |                 |\n|    |              |  GROUP    |         | GROUP BY id                                     |                 |\n|    |              |  ORDER    |         | ORDER BY .. DESC                                |                 |\n|    |              |  LIMIT    |         | LIMIT 10                                        |                 |\n| 00 | &#91;REDIST(id)] |  Table    | t1&#91;DIS] |                                                 | t1              |\n|    |              |  GROUP    |         | GROUP BY id                                     |                 |\n+----+--------------+-----------+---------+-------------------------------------------------+-----------------+\n9 rows in set (Elapsed: 00:00:00.00)\n<\/code><\/pre>\n\n\n\n<h3 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Hash%E5%88%86%E5%B8%83%E8%A1%A8-2\"><\/span>Hash\u5206\u5e03\u8868<span class=\"ez-toc-section-end\"><\/span><\/h3>\n\n\n\n<h4 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"%E8%81%9A%E5%90%88%E5%88%97%E4%B8%8D%E5%8C%85%E5%90%ABHash%E5%88%86%E5%B8%83%E5%88%97\"><\/span>\u805a\u5408\u5217\u4e0d\u5305\u542bHash\u5206\u5e03\u5217<span class=\"ez-toc-section-end\"><\/span><\/h4>\n\n\n\n<p>\u5219\u548c\u968f\u673a\u5206\u5e03\u8868\u4e00\u6837\u3002<\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"899\" height=\"233\" src=\"https:\/\/www.gbase8.cn\/wp-content\/uploads\/2021\/02\/image-3.png\" alt=\"GBase 8a \u6267\u884c\u8ba1\u5212explian \u805a\u5408\u5217\u4e0d\u5305\u542bHash\u5206\u5e03\u5217\" class=\"wp-image-4179\"\/><figcaption>GBase 8a \u6267\u884c\u8ba1\u5212explian \u805a\u5408\u5217\u4e0d\u5305\u542bHash\u5206\u5e03\u5217<\/figcaption><\/figure>\n\n\n\n<pre class=\"wp-block-code\"><code>gbase&gt; explain select name,count(*) from td group by name order by count(*) desc limit 10;\n+----+----------------+-----------+--------+-------------------------------------------------+-----------------+\n| ID | MOTION         | OPERATION | TABLE  | CONDITION                                       | NO STAT Tab\/Col |\n+----+----------------+-----------+--------+-------------------------------------------------+-----------------+\n| 02 | &#91;RESULT]       |  Step     | &lt;01&gt;   |                                                 |                 |\n|    |                |  ORDER    |        | ORDER BY cast(SUM_2ND(COUNT(0)) as signed) DESC |                 |\n|    |                |  LIMIT    |        | LIMIT 10                                        |                 |\n| 01 | &#91;GATHER]       |  Step     | &lt;00&gt;   |                                                 |                 |\n|    |                |  GROUP    |        | GROUP BY name                                   |                 |\n|    |                |  ORDER    |        | ORDER BY .. DESC                                |                 |\n|    |                |  LIMIT    |        | LIMIT 10                                        |                 |\n| 00 | &#91;REDIST(name)] |  Table    | td&#91;id] |                                                 | td              |\n|    |                |  GROUP    |        | GROUP BY name                                   |                 |\n+----+----------------+-----------+--------+-------------------------------------------------+-----------------+\n9 rows in set (Elapsed: 00:00:00.02)\n<\/code><\/pre>\n\n\n\n<h4 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"%E8%81%9A%E5%90%88%E5%88%97%E5%8C%85%E5%90%ABHash%E5%88%86%E5%B8%83%E5%88%97\"><\/span>\u805a\u5408\u5217\u5305\u542bHash\u5206\u5e03\u5217<span class=\"ez-toc-section-end\"><\/span><\/h4>\n\n\n\n<p>\u5219\u7701\u6389\u4e86\u91cd\u5206\u5e03\u6b65\u9aa4\u3002<\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"784\" height=\"200\" src=\"https:\/\/www.gbase8.cn\/wp-content\/uploads\/2021\/02\/image-1.png\" alt=\"GBase 8a \u6267\u884c\u8ba1\u5212explian \u805a\u5408\u5217\u5305\u542bHash\u5206\u5e03\u5217\" class=\"wp-image-4170\"\/><figcaption>GBase 8a \u6267\u884c\u8ba1\u5212explian \u805a\u5408\u5217\u5305\u542bHash\u5206\u5e03\u5217<\/figcaption><\/figure>\n\n\n\n<ul class=\"wp-block-list\"><li>00\uff1a \u672c\u5730\u505a\u5206\u7ec4\uff0c\u5e76\u8fd4\u56de\u6709\u9650\u6392\u5e8f\u7ed3\u679c(order limit), \u7ed3\u679c\u53d1\u5230\u6c47\u603b\u8868[GATHER]<\/li><li>01\uff1a\u91c7\u752800\u7684\u6c47\u603b\u8868\uff0c\u505a\u4e8c\u6b21\u6709\u9650\u7ed3\u679c\u96c6\u6392\u5e8f\uff0c\u5e76\u8fd4\u56de\u8c03\u7528\u7aef[RESULT]<\/li><\/ul>\n\n\n\n<pre class=\"wp-block-code\"><code>gbase&gt; explain select id,count(*) from td group by id order by count(*) desc limit 10;\n+----+----------+-----------+--------+----------------------------------------+-----------------+\n| ID | MOTION   | OPERATION | TABLE  | CONDITION                              | NO STAT Tab\/Col |\n+----+----------+-----------+--------+----------------------------------------+-----------------+\n| 01 | &#91;RESULT] |  Step     | &lt;00&gt;   |                                        |                 |\n|    |          |  ORDER    |        | ORDER BY cast(COUNT(0) as signed) DESC |                 |\n|    |          |  LIMIT    |        | LIMIT 10                               |                 |\n| 00 | &#91;GATHER] |  Table    | td&#91;id] |                                        | td              |\n|    |          |  GROUP    |        | GROUP BY id                            |                 |\n|    |          |  ORDER    |        | ORDER BY .. DESC                       |                 |\n|    |          |  LIMIT    |        | LIMIT 10                               |                 |\n+----+----------+-----------+--------+----------------------------------------+-----------------+\n7 rows in set (Elapsed: 00:00:00.01)\n<\/code><\/pre>\n\n\n\n<h3 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"%E5%A4%8D%E5%88%B6%E8%A1%A8-2\"><\/span>\u590d\u5236\u8868<span class=\"ez-toc-section-end\"><\/span><\/h3>\n\n\n\n<p>\u590d\u5236\u8868\u90fd\u662f\u4e00\u6b65\u76f4\u63a5\u51fa\u7ed3\u679c\u8fd4\u56de\u8c03\u7528\u7aef\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>gbase> explain select id,count(*) from tr group by id order by count(*) desc limit 10;\r\n+----+----------+-----------+---------+------------------+-----------------+\r\n| ID | MOTION   | OPERATION | TABLE   | CONDITION        | NO STAT Tab\/Col |\r\n+----+----------+-----------+---------+------------------+-----------------+\r\n| 00 | &#91;RESULT] |  Table    | tr&#91;REP] |                  | tr              |\r\n|    |          |  GROUP    |         | GROUP BY id      |                 |\r\n|    |          |  ORDER    |         | ORDER BY .. DESC |                 |\r\n|    |          |  LIMIT    |         | LIMIT 10         |                 |\r\n+----+----------+-----------+---------+------------------+-----------------+\r\n4 rows in set (Elapsed: 00:00:00.01)\r\n<\/code><\/pre>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"%E3%80%90%E5%88%9D%E3%80%91UNION%E6%93%8D%E4%BD%9C\"><\/span>\u3010\u521d\u3011UNION\u64cd\u4f5c<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p>\u6bcf\u4e2a\u8282\u70b9\u5404\u81ea\u505aunion\u53bb\u91cd\uff0c\u7136\u540e\u53d1\u9001\u5230\u6c47\u603b\u8868\u3002<\/p>\n\n\n\n<h3 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"2%E4%B8%AA%E9%9A%8F%E6%9C%BA%E5%88%86%E5%B8%83%E8%A1%A8%E5%81%9Aunion\"><\/span>2\u4e2a\u968f\u673a\u5206\u5e03\u8868\u505aunion<span class=\"ez-toc-section-end\"><\/span><\/h3>\n\n\n\n<ul class=\"wp-block-list\"><li>00\uff1at1\u548ctd\u505aunion\u53bb\u91cd\uff0c\u53d1\u9001\u5230\u6c47\u603b\u8868[GATHER]<\/li><li>01\uff1a\u91c7\u752800\u7684\u6c47\u603b\u8868\uff0c\u518d\u6b21\u53bb\u91cd(distinct)\u5e76\u8fd4\u56de[RESULT]<\/li><\/ul>\n\n\n\n<pre class=\"wp-block-code\"><code>gbase&gt; explain select id from t1 union select id from td;\n+----+----------+-----------+---------+-----------+-----------------+\n| ID | MOTION   | OPERATION | TABLE   | CONDITION | NO STAT Tab\/Col |\n+----+----------+-----------+---------+-----------+-----------------+\n| 01 | &#91;RESULT] |  Step     | &lt;00&gt;    |           |                 |\n|    |          |  AGG      |         |           |                 |\n| 00 | &#91;GATHER] |  Table    | t1&#91;DIS] |           | t1              |\n|    |          |  UNION    |         |           | td              |\n|    |          |  Table    | td&#91;id]  |           |                 |\n+----+----------+-----------+---------+-----------+-----------------+\n5 rows in set (Elapsed: 00:00:00.01)\n<\/code><\/pre>\n\n\n\n<h3 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"2%E4%B8%AAHash%E5%88%86%E5%B8%83%E8%A1%A8%E5%81%9Aunion\"><\/span>2\u4e2aHash\u5206\u5e03\u8868\u505aunion<span class=\"ez-toc-section-end\"><\/span><\/h3>\n\n\n\n<p>\u76f4\u63a5\u672c\u5730union\u5373\u53ef\uff0c\u7ed3\u679c\u8fd4\u56de\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>gbase> explain select * from td union select * from td_2;\r\n+----+----------+-----------+----------+-----------+-----------------+\r\n| ID | MOTION   | OPERATION | TABLE    | CONDITION | NO STAT Tab\/Col |\r\n+----+----------+-----------+----------+-----------+-----------------+\r\n| 00 | &#91;RESULT] |  Table    | td&#91;id]   |           | td              |\r\n|    |          |  UNION    |          |           | td_2            |\r\n|    |          |  Table    | td_2&#91;id] |           |                 |\r\n+----+----------+-----------+----------+-----------+-----------------+\r\n3 rows in set (Elapsed: 00:00:00.01)\r\n<\/code><\/pre>\n\n\n\n<h3 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"1%E4%B8%AAHash%E5%92%8C1%E4%B8%AA%E9%9A%8F%E6%9C%BA%E5%88%86%E5%B8%83%E8%A1%A8union\"><\/span>1\u4e2aHash\u548c1\u4e2a\u968f\u673a\u5206\u5e03\u8868union<span class=\"ez-toc-section-end\"><\/span><\/h3>\n\n\n\n<p>\u5404\u8282\u70b9\u5206\u522b\u505aunion,\u5e76\u5c06\u7ed3\u679c\u53d1\u9001\u5230\u6c47\u603b\u8868\uff0c\u6700\u540e\u5728\u6c47\u603b\u8868\u505a\u53bb\u91cd\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>gbase> explain select * from t1 union select * from td;\r\n+----+----------+-----------+---------+-----------+-----------------+\r\n| ID | MOTION   | OPERATION | TABLE   | CONDITION | NO STAT Tab\/Col |\r\n+----+----------+-----------+---------+-----------+-----------------+\r\n| 01 | &#91;RESULT] |  Step     | &lt;00>    |           |                 |\r\n|    |          |  AGG      |         |           |                 |\r\n| 00 | &#91;GATHER] |  Table    | t1&#91;DIS] |           | t1              |\r\n|    |          |  UNION    |         |           | td              |\r\n|    |          |  Table    | td&#91;id]  |           |                 |\r\n+----+----------+-----------+---------+-----------+-----------------+\r\n5 rows in set (Elapsed: 00:00:00.00)\r\n<\/code><\/pre>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"%E3%80%90%E4%B8%AD%E3%80%91%E5%B8%A6%E5%8D%95%E7%BA%AFcount%EF%BC%88%EF%BC%89%E7%9A%84union\"><\/span>\u3010\u4e2d\u3011\u5e26\u5355\u7eafcount\uff08*\uff09\u7684union<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p>union\u64cd\u4f5c\u672c\u8eab\u6709\u53bb\u91cd\u529f\u80fd\uff0c\u6240\u4ee5\u9700\u8981\u5c06\u6bcf\u4e2a\u53c2\u4e0e\u7684\u8868\u90fd\u5404\u81ea\u805a\u5408\u540e\uff0c\u518dunion\u53bb\u91cd\uff0c\u53d1\u9001\u5230\u6c47\u603b\u8868\uff0c\u6700\u540e\u518d\u6b21\u6c47\u603b\u4e09\u6b65\uff1b<\/p>\n\n\n\n<ul class=\"wp-block-list\"><li>00\uff1at1\u8868\u805a\u5408\uff0c\u7136\u540e\u53d1\u5230\u6c47\u603b\u8868[GATHER]<\/li><li>01\uff1atd\u8868\u805a\u5408\uff0c\u7136\u540e\u53d1\u5230\u6c47\u603b\u8868[GATHER]<\/li><li>02\uff1a\u752800\u7684\u8868\u548c01\u7684\u8868\u518d\u6b21\u805a\u5408\u5e76\u8fd4\u56de[RESULT]<\/li><\/ul>\n\n\n\n<pre class=\"wp-block-code\"><code>gbase> explain select count(*) from t1 union select count(*) from td;\r\n+----+----------+-----------+---------+-----------+-----------------+\r\n| ID | MOTION   | OPERATION | TABLE   | CONDITION | NO STAT Tab\/Col |\r\n+----+----------+-----------+---------+-----------+-----------------+\r\n| 02 | &#91;RESULT] |  Step     | &lt;00>    |           |                 |\r\n|    |          |  AGG      |         |           |                 |\r\n|    |          |  UNION    |         |           |                 |\r\n|    |          |  Step     | &lt;01>    |           |                 |\r\n|    |          |  AGG      |         |           |                 |\r\n| 01 | &#91;GATHER] |  Table    | td&#91;id]  |           |                 |\r\n|    |          |  AGG      |         |           |                 |\r\n| 00 | &#91;GATHER] |  Table    | t1&#91;DIS] |           | t1              |\r\n|    |          |  AGG      |         |           | td              |\r\n+----+----------+-----------+---------+-----------+-----------------+\r\n9 rows in set (Elapsed: 00:00:00.00)\r\n<\/code><\/pre>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"%E3%80%90%E4%B8%AD%E3%80%91%E5%B8%A6%E8%81%9A%E5%90%88GROUP%E7%9A%84union\"><\/span>\u3010\u4e2d\u3011\u5e26\u805a\u5408GROUP\u7684union<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p>\u672c\u4f8b\u4e5f\u662f\u4e00\u4e2a\u591a\u4e2a\u64cd\u4f5c\u5408\u5e76\u7684\u4f8b\u5b50\uff0c\u4e5f\u662f\u5e38\u89c1\u64cd\u4f5c\u3002<\/p>\n\n\n\n<h3 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"2%E4%B8%AA%E9%9A%8F%E6%9C%BA%E5%88%86%E5%B8%83%E8%A1%A8%E8%81%9A%E5%90%88%E7%BB%93%E6%9E%9C%E7%9A%84union%E3%80%82\"><\/span>2\u4e2a\u968f\u673a\u5206\u5e03\u8868\u805a\u5408\u7ed3\u679c\u7684union\u3002<span class=\"ez-toc-section-end\"><\/span><\/h3>\n\n\n\n<ul class=\"wp-block-list\"><li>00\uff1at1\u8868\u805a\u5408\u540e\u5206\u53d1\u5230Hash\u5206\u5e03\u8868[REDIST]<\/li><li>01\uff1at1_2\u8868\u805a\u5408\u540e\u5206\u53d1\u5230Hash\u5206\u5e03\u8868[REDIST]<\/li><li>02\uff1a00\u7684Hash\u5206\u5e03\u8868\u548c01\u7684Hash\u5206\u5e03\u8868\uff0c\u518d\u6b21\u505a\u805a\u5408GROUP\u5e76union \u64cd\u4f5c\uff0c\u7ed3\u679c\u53d1\u9001\u5ba2\u6237\u7aef[RESULT]<\/li><\/ul>\n\n\n\n<pre class=\"wp-block-code\"><code>gbase> explain select id,count(*) from t1 group by id union all select id,count(*) from t1_2 group by id;\r\n+----+--------------+------------+-----------+-------------+-----------------+\r\n| ID | MOTION       | OPERATION  | TABLE     | CONDITION   | NO STAT Tab\/Col |\r\n+----+--------------+------------+-----------+-------------+-----------------+\r\ngbase> explain select id,count(*) from t1 group by id union select id,count(*) from t1_2 group by id;\r\n+----+--------------+-----------+-----------+-------------+-----------------+\r\n| ID | MOTION       | OPERATION | TABLE     | CONDITION   | NO STAT Tab\/Col |\r\n+----+--------------+-----------+-----------+-------------+-----------------+\r\n| 02 | &#91;RESULT]     |  Step     | &lt;00>      |             |                 |\r\n|    |              |  GROUP    |           | GROUP BY id |                 |\r\n|    |              |  UNION    |           |             |                 |\r\n|    |              |  Step     | &lt;01>      |             |                 |\r\n|    |              |  GROUP    |           | GROUP BY id |                 |\r\n| 01 | &#91;REDIST(id)] |  Table    | t1_2&#91;DIS] |             |                 |\r\n|    |              |  GROUP    |           | GROUP BY id |                 |\r\n| 00 | &#91;REDIST(id)] |  Table    | t1&#91;DIS]   |             | t1              |\r\n|    |              |  GROUP    |           | GROUP BY id | t1_2            |\r\n+----+--------------+-----------+-----------+-------------+-----------------+\r\n9 rows in set (Elapsed: 00:00:00.01)\r<\/code><\/pre>\n\n\n\n<h3 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"2%E4%B8%AAHash%E5%88%86%E5%B8%83%E8%A1%A8%E8%81%9A%E5%90%88%E5%8C%85%E5%90%ABHash%E5%88%86%E5%B8%83%E5%88%97%E7%9A%84union\"><\/span>2\u4e2aHash\u5206\u5e03\u8868\u805a\u5408\u5305\u542bHash\u5206\u5e03\u5217\u7684union<span class=\"ez-toc-section-end\"><\/span><\/h3>\n\n\n\n<p>\u56e0\u4e3a2\u4e2a\u8868\u90fd\u662fHash\u5206\u5e03\u8868\u4e14\u5305\u542b\u5728\u805a\u5408\u5217\u5185\uff0c\u6240\u4ee5\u5404\u8282\u70b9\u5206\u522b\u505a\u805a\u5408\u548cunion\u64cd\u4f5c\u540e\uff0c\u76f4\u63a5\u8fd4\u56de\u5373\u53ef\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>gbase&gt; explain select id,count(*) from td group by id union select id,count(*) from td_2 group by id;\n+----+----------+-----------+----------+-------------+-----------------+\n| ID | MOTION   | OPERATION | TABLE    | CONDITION   | NO STAT Tab\/Col |\n+----+----------+-----------+----------+-------------+-----------------+\n| 00 | &#91;RESULT] |  Table    | td&#91;id]   |             | td              |\n|    |          |  GROUP    |          | GROUP BY id | td_2            |\n|    |          |  UNION    |          |             |                 |\n|    |          |  Table    | td_2&#91;id] |             |                 |\n|    |          |  GROUP    |          | GROUP BY id |                 |\n+----+----------+-----------+----------+-------------+-----------------+\n5 rows in set (Elapsed: 00:00:00.00)\n<\/code><\/pre>\n\n\n\n<h3 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"%E9%9A%8F%E6%9C%BA%E5%88%86%E5%B8%83%E8%A1%A8%E5%92%8CHash%E5%88%86%E5%B8%83%E8%A1%A8%E5%8C%85%E5%90%AB%E5%9C%A8%E8%81%9A%E5%90%88%E5%88%97%E7%9A%84union\"><\/span>\u968f\u673a\u5206\u5e03\u8868\u548cHash\u5206\u5e03\u8868\u5305\u542b\u5728\u805a\u5408\u5217\u7684union<span class=\"ez-toc-section-end\"><\/span><\/h3>\n\n\n\n<p>\u6839\u636e\u5168\u9762\u4ecb\u7ecd\uff0c\u968f\u673a\u5206\u5e03\u8868\u5c06\u5148\u505a\u805a\u5408\u540e\u7684\u91cd\u5206\u5e03\uff0c\u7136\u540e\u518d\u4e0eHash\u5206\u5e03\u8868\u505a\u672c\u5730\u7684\u4e8c\u6b21\u805a\u5408\u548cunion\u3002<\/p>\n\n\n\n<ul class=\"wp-block-list\"><li>00\uff1at1\u968f\u673a\u5206\u5e03\u8868\u505a\u805a\u5408\uff0c\u7136\u540e\u53d1\u9001\u5230Hash\u5206\u5e03\u8868<\/li><li>01\uff1a\u4f7f\u752800\u7684Hash\u5206\u5e03\u8868\uff0c\u4e0eHash\u5206\u5e03\u8868td\u505a\u805a\u5408\u548cunion\u64cd\u4f5c\uff0c\u7136\u540e\u8fd4\u56de[RESULT]<\/li><\/ul>\n\n\n\n<pre class=\"wp-block-code\"><code>gbase&gt; explain select id,count(*) from t1 group by id union select id,count(*) from td group by id;\n+----+--------------+-----------+---------+-------------+-----------------+\n| ID | MOTION       | OPERATION | TABLE   | CONDITION   | NO STAT Tab\/Col |\n+----+--------------+-----------+---------+-------------+-----------------+\n| 01 | &#91;RESULT]     |  Step     | &lt;00&gt;    |             |                 |\n|    |              |  GROUP    |         | GROUP BY id |                 |\n|    |              |  UNION    |         |             |                 |\n|    |              |  Table    | td&#91;id]  |             |                 |\n|    |              |  GROUP    |         | GROUP BY id |                 |\n| 00 | &#91;REDIST(id)] |  Table    | t1&#91;DIS] |             | t1              |\n|    |              |  GROUP    |         | GROUP BY id | td              |\n+----+--------------+-----------+---------+-------------+-----------------+\n7 rows in set (Elapsed: 00:00:00.04)<\/code><\/pre>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"%E3%80%90%E5%88%9D%E3%80%91UNION_ALL_%E6%93%8D%E4%BD%9C\"><\/span>\u3010\u521d\u3011UNION ALL \u64cd\u4f5c<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p>union all\u4e0d\u9700\u8981\u53bb\u91cd\uff0c\u6267\u884c\u8ba1\u5212\u660e\u663e\u7b80\u5355\u4e86\u5f88\u591a\u3002\u5168\u90e8\u90fd\u662f\u5404\u8282\u70b9\u505aunion all\uff0c \u7136\u540e\u8fd4\u56de\u5373\u53ef\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>gbase> explain select * from t1 union all select * from t1_2;\r\n+----+----------+------------+-----------+-----------+-----------------+\r\n| ID | MOTION   | OPERATION  | TABLE     | CONDITION | NO STAT Tab\/Col |\r\n+----+----------+------------+-----------+-----------+-----------------+\r\n| 00 | &#91;RESULT] |  Table     | t1&#91;DIS]   |           | t1              |\r\n|    |          |  UNION ALL |           |           | t1_2            |\r\n|    |          |  Table     | t1_2&#91;DIS] |           |                 |\r\n+----+----------+------------+-----------+-----------+-----------------+\r\n3 rows in set (Elapsed: 00:00:00.01)\r\n\ngbase> explain select * from t1 union all select * from td;\r\n+----+----------+------------+---------+-----------+-----------------+\r\n| ID | MOTION   | OPERATION  | TABLE   | CONDITION | NO STAT Tab\/Col |\r\n+----+----------+------------+---------+-----------+-----------------+\r\n| 00 | &#91;RESULT] |  Table     | t1&#91;DIS] |           | t1              |\r\n|    |          |  UNION ALL |         |           | td              |\r\n|    |          |  Table     | td&#91;id]  |           |                 |\r\n+----+----------+------------+---------+-----------+-----------------+\r\n3 rows in set (Elapsed: 00:00:00.01)\r\n\r\ngbase> explain select * from td union all select * from td_2;\r\n+----+----------+------------+----------+-----------+-----------------+\r\n| ID | MOTION   | OPERATION  | TABLE    | CONDITION | NO STAT Tab\/Col |\r\n+----+----------+------------+----------+-----------+-----------------+\r\n| 00 | &#91;RESULT] |  Table     | td&#91;id]   |           | td              |\r\n|    |          |  UNION ALL |          |           | td_2            |\r\n|    |          |  Table     | td_2&#91;id] |           |                 |\r\n+----+----------+------------+----------+-----------+-----------------+\r\n3 rows in set (Elapsed: 00:00:00.00)\r<\/code><\/pre>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"%E3%80%90%E4%B8%AD%E3%80%912%E8%A1%A8join%E6%93%8D%E4%BD%9C\"><\/span>\u3010\u4e2d\u30112\u8868join\u64cd\u4f5c<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<h3 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Hash%E5%88%86%E5%B8%83%E8%A1%A8%E4%B8%94join%E5%88%97%E4%B8%BAHash%E5%88%86%E5%B8%83%E5%88%97\"><\/span>Hash\u5206\u5e03\u8868\u4e14join\u5217\u4e3aHash\u5206\u5e03\u5217<span class=\"ez-toc-section-end\"><\/span><\/h3>\n\n\n\n<p>\u56e0\u4e3aHash\u5206\u5e03\u5217\u4e5f\u662fJoin\u7684\u6761\u4ef6\u5217(\u5305\u542b\u5728JOIN\u6761\u4ef6\u4e2d\u5373\u53ef\uff0c\u65e0\u9700\u552f\u4e00\uff09\uff0c\u65e0\u8bba\u54ea\u79cdjoin,\u90fd\u662f\u672c\u5730\u8fd0\u884c\uff0c\u7136\u540e\u8fd4\u56de\u7ed3\u679c\u5373\u53ef\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>gbase> explain select * from td left join td_2 on td.id=td_2.id;\r\n+----+----------+------------+----------+-----------+-----------------+\r\n| ID | MOTION   | OPERATION  | TABLE    | CONDITION | NO STAT Tab\/Col |\r\n+----+----------+------------+----------+-----------+-----------------+\r\n| 00 | &#91;RESULT] |  LEFT JOIN |          | (id = id) | td              |\r\n|    |          |   Table    | td&#91;id]   |           |                 |\r\n|    |          |   Table    | td_2&#91;id] |           |                 |\r\n+----+----------+------------+----------+-----------+-----------------+\r\n3 rows in set (Elapsed: 00:00:00.00)\r\n\r\ngbase> explain select * from td right join td_2 on td.id=td_2.id;\r\n+----+----------+------------+----------+-----------+-----------------+\r\n| ID | MOTION   | OPERATION  | TABLE    | CONDITION | NO STAT Tab\/Col |\r\n+----+----------+------------+----------+-----------+-----------------+\r\n| 00 | &#91;RESULT] |  LEFT JOIN |          | (id = id) | td_2            |\r\n|    |          |   Table    | td_2&#91;id] |           |                 |\r\n|    |          |   Table    | td&#91;id]   |           |                 |\r\n+----+----------+------------+----------+-----------+-----------------+\r\n3 rows in set (Elapsed: 00:00:00.00)\r\n\r\ngbase> explain select * from td inner join td_2 on td.id=td_2.id;\r\n+----+----------+-------------+----------+-----------+-----------------+\r\n| ID | MOTION   | OPERATION   | TABLE    | CONDITION | NO STAT Tab\/Col |\r\n+----+----------+-------------+----------+-----------+-----------------+\r\n| 00 | &#91;RESULT] |  INNER JOIN |          | (id = id) | td_2            |\r\n|    |          |   Table     | td_2&#91;id] |           |                 |\r\n|    |          |   Table     | td&#91;id]   |           |                 |\r\n+----+----------+-------------+----------+-----------+-----------------+\r\n3 rows in set (Elapsed: 00:00:00.01)\r\n<\/code><\/pre>\n\n\n\n<h3 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Hash%E5%88%86%E5%B8%83%E5%A4%A7%E8%A1%A8%E5%92%8C%E9%9A%8F%E6%9C%BA%E5%88%86%E5%B8%83%E5%A4%A7%E8%A1%A8JOIN\"><\/span>Hash\u5206\u5e03\u5927\u8868\u548c\u968f\u673a\u5206\u5e03\u5927\u8868JOIN<span class=\"ez-toc-section-end\"><\/span><\/h3>\n\n\n\n<p>\u5927\u8868\u6307\u6570\u636e\u91cf\u8d85\u8fc7\u53c2\u6570\u7684\u8868\uff0c\u8be5\u53c2\u6570\u901a\u8fc7gcluster_hash_redist_threshold_row\u8bbe\u7f6e\uff0c\u4e5f\u5c31\u662f\u5982\u679c\u5c0f\u4e8e\u8fd9\u4e2a\u6570\u503c\uff0c\u662f\u53ef\u80fd\u88ab\u62c9\u6210\u590d\u5236\u8868\u7684\u3002\u5bf9\u5404\u79cdJOIIN\u7c7b\u578b\u65e0\u533a\u522b\u3002<\/p>\n\n\n\n<ul class=\"wp-block-list\"><li>00\uff1a\u968f\u673a\u5206\u5e03\u8868t1\u6839\u636eid\u8fdb\u884cHash\u91cd\u5206\u5e03\u3002<\/li><li>01\uff1a\u4f7f\u752800\u7684\u7ed3\u679c\u8868\uff0c\u4e0eHash\u5206\u5e03\u8868td\u8fdb\u884c\u672c\u5730join,\u7136\u540e\u8fd4\u56de\u7ed3\u679c\u3002<\/li><\/ul>\n\n\n\n<pre class=\"wp-block-code\"><code>gbase> explain select * from t1 left join td on t1.id=td.id;\r\n+----+--------------+------------+---------+-----------+-----------------+\r\n| ID | MOTION       | OPERATION  | TABLE   | CONDITION | NO STAT Tab\/Col |\r\n+----+--------------+------------+---------+-----------+-----------------+\r\n| 01 | &#91;RESULT]     |  LEFT JOIN |         | (id = id) |                 |\r\n|    |              |   Step     | &lt;00>    |           |                 |\r\n|    |              |   Table    | td&#91;id]  |           |                 |\r\n| 00 | &#91;REDIST(id)] |  Table     | t1&#91;DIS] |           | t1              |\r\n+----+--------------+------------+---------+-----------+-----------------+\r\n4 rows in set (Elapsed: 00:00:00.64)\r\n\r\ngbase> explain select * from t1 right join td on t1.id=td.id;\r\n+----+--------------+------------+---------+-----------+-----------------+\r\n| ID | MOTION       | OPERATION  | TABLE   | CONDITION | NO STAT Tab\/Col |\r\n+----+--------------+------------+---------+-----------+-----------------+\r\n| 01 | &#91;RESULT]     |  LEFT JOIN |         | (id = id) |                 |\r\n|    |              |   Table    | td&#91;id]  |           |                 |\r\n|    |              |   Step     | &lt;00>    |           |                 |\r\n| 00 | &#91;REDIST(id)] |  Table     | t1&#91;DIS] |           | td              |\r\n+----+--------------+------------+---------+-----------+-----------------+\r\n4 rows in set (Elapsed: 00:00:00.79)\r\n\ngbase> explain select * from t1 inner join td on t1.id=td.id;\r\n+----+--------------+-------------+---------+-----------+-----------------+\r\n| ID | MOTION       | OPERATION   | TABLE   | CONDITION | NO STAT Tab\/Col |\r\n+----+--------------+-------------+---------+-----------+-----------------+\r\n| 01 | &#91;RESULT]     |  INNER JOIN |         | (id = id) |                 |\r\n|    |              |   Step      | &lt;00>    |           |                 |\r\n|    |              |   Table     | td&#91;id]  |           |                 |\r\n| 00 | &#91;REDIST(id)] |  Table      | t1&#91;DIS] |           | t1              |\r\n+----+--------------+-------------+---------+-----------+-----------------+\r\n4 rows in set (Elapsed: 00:00:00.25)\r\n<\/code><\/pre>\n\n\n\n<h3 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"2%E4%B8%AA%E5%A4%A7%E7%9A%84%E9%9A%8F%E6%9C%BA%E5%88%86%E5%B8%83%E8%A1%A8%E5%81%9AJoin\"><\/span>2\u4e2a\u5927\u7684\u968f\u673a\u5206\u5e03\u8868\u505aJoin<span class=\"ez-toc-section-end\"><\/span><\/h3>\n\n\n\n<p>\u5982\u4e0b\u4f8b\u5b50\u91c7\u7528name\u5217\u505ajoin\u6761\u4ef6\uff0c\u9700\u8981\u5148\u5c062\u4e2a\u8868\u5206\u522b\u505a\u52a8\u6001\u91cd\u5206\u5e03\uff0c\u7136\u540e\u518d\u672c\u5730join\u8fd4\u56de\u3002\u5404\u79cdJOIN\u7c7b\u578b\u6ca1\u533a\u522b\u3002<\/p>\n\n\n\n<ul class=\"wp-block-list\"><li>00\uff1atd\u867d\u7136\u662fHash\u5206\u5e03\u8868\u4f46JOIN\u5217\u4e0d\u662fHash\u5206\u5e03\u5217\uff0c\u6839\u636ename\u5217\u505a\u52a8\u6001\u91cd\u5206\u5e03\u3002<\/li><li>01\uff1at1\u662f\u968f\u673a\u5206\u5e03\u8868\uff0c\u6839\u636ename\u505a\u52a8\u6001\u91cd\u5206\u5e03<\/li><li>02\uff1a\u91c7\u752800\u548c01\u7684\u8868\uff0c\u505a\u672c\u5730join\u5e76\u8fd4\u56de\u7ed3\u679c<\/li><\/ul>\n\n\n\n<pre class=\"wp-block-code\"><code>gbase> explain select * from t1 left join td on t1.name=td.name;\r\n+----+----------------+------------+---------+---------------+-----------------+\r\n| ID | MOTION         | OPERATION  | TABLE   | CONDITION     | NO STAT Tab\/Col |\r\n+----+----------------+------------+---------+---------------+-----------------+\r\n| 02 | &#91;RESULT]       |  LEFT JOIN |         | (name = name) |                 |\r\n|    |                |   Step     | &lt;00>    |               |                 |\r\n|    |                |   Step     | &lt;01>    |               |                 |\r\n| 01 | &#91;REDIST(name)] |  Table     | td&#91;id]  |               |                 |\r\n| 00 | &#91;REDIST(name)] |  Table     | t1&#91;DIS] |               | t1              |\r\n+----+----------------+------------+---------+---------------+-----------------+\r\n5 rows in set (Elapsed: 00:00:00.89)\r\n\ngbase> explain select * from t1 right join td on t1.name=td.name;\r\n+----+----------------+------------+---------+---------------+-----------------+\r\n| ID | MOTION         | OPERATION  | TABLE   | CONDITION     | NO STAT Tab\/Col |\r\n+----+----------------+------------+---------+---------------+-----------------+\r\n| 02 | &#91;RESULT]       |  LEFT JOIN |         | (name = name) |                 |\r\n|    |                |   Step     | &lt;00>    |               |                 |\r\n|    |                |   Step     | &lt;01>    |               |                 |\r\n| 01 | &#91;REDIST(name)] |  Table     | t1&#91;DIS] |               |                 |\r\n| 00 | &#91;REDIST(name)] |  Table     | td&#91;id]  |               | td              |\r\n+----+----------------+------------+---------+---------------+-----------------+\r\n5 rows in set (Elapsed: 00:00:00.37)\r\n\ngbase> explain select * from t1 inner join td on t1.name=td.name;\r\n+----+----------------+-------------+---------+---------------+-----------------+\r\n| ID | MOTION         | OPERATION   | TABLE   | CONDITION     | NO STAT Tab\/Col |\r\n+----+----------------+-------------+---------+---------------+-----------------+\r\n| 02 | &#91;RESULT]       |  INNER JOIN |         | (name = name) |                 |\r\n|    |                |   Step      | &lt;00>    |               |                 |\r\n|    |                |   Step      | &lt;01>    |               |                 |\r\n| 01 | &#91;REDIST(name)] |  Table      | td&#91;id]  |               |                 |\r\n| 00 | &#91;REDIST(name)] |  Table      | t1&#91;DIS] |               | t1              |\r\n+----+----------------+-------------+---------+---------------+-----------------+\r\n5 rows in set (Elapsed: 00:00:00.50)\r\n<\/code><\/pre>\n\n\n\n<h3 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"%E5%A4%A7%E7%9A%84%E9%9A%8F%E6%9C%BA%E5%88%86%E5%B8%83%E8%A1%A8%E5%92%8C%E5%B0%8F%E7%9A%84%E9%9A%8F%E6%9C%BA%E5%88%86%E5%B8%83%E8%A1%A8%E5%81%9AJOIN\"><\/span>\u5927\u7684\u968f\u673a\u5206\u5e03\u8868\u548c\u5c0f\u7684\u968f\u673a\u5206\u5e03\u8868\u505aJOIN<span class=\"ez-toc-section-end\"><\/span><\/h3>\n\n\n\n<p>\u56e0\u4e3a\u65f6\u5927\u5c0f\u8868\uff0c\u533a\u5206JOIN\u7c7b\u578b\u3002<\/p>\n\n\n\n<h4 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"LEFT_JOIN_%E5%B0%8F%E8%A1%A8%E6%8B%89%E5%A4%8D%E5%88%B6%E8%A1%A8\"><\/span>LEFT JOIN \u5c0f\u8868\u62c9\u590d\u5236\u8868<span class=\"ez-toc-section-end\"><\/span><\/h4>\n\n\n\n<p>\u56e0\u4e3at1_2\u53ea\u67091000\u884c\uff0c\u800ct1\u67093300\u4e07\uff0c\u6240\u4ee5\u5c0f\u8868\u62c9\u4e86\u590d\u5236\u8868\u3002<\/p>\n\n\n\n<ul class=\"wp-block-list\"><li>00\uff1at1_2\u5c0f\u8868\u62c9\u4e86\u590d\u5236\u8868[BROADCAST]<\/li><li>01\uff1a\u91c7\u7528\u5927\u7684\u968f\u673a\u5206\u5e03\u8868t1\u548c00\u7684\u590d\u5236\u8868\u505aJOIN\u5e76\u8fd4\u56de\u7ed3\u679c<\/li><\/ul>\n\n\n\n<pre class=\"wp-block-code\"><code>gbase> explain select * from t1 left join t1_2 on t1.name=t1_2.name;\r\n+----+-------------+------------+-----------+---------------+-----------------+\r\n| ID | MOTION      | OPERATION  | TABLE     | CONDITION     | NO STAT Tab\/Col |\r\n+----+-------------+------------+-----------+---------------+-----------------+\r\n| 01 | &#91;RESULT]    |  LEFT JOIN |           | (name = name) |                 |\r\n|    |             |   Table    | t1&#91;DIS]   |               |                 |\r\n|    |             |   Step     | &lt;00>      |               |                 |\r\n| 00 | &#91;BROADCAST] |  Table     | t1_2&#91;DIS] |               | t1              |\r\n+----+-------------+------------+-----------+---------------+-----------------+\r\n4 rows in set (Elapsed: 00:00:00.77)\r\n<\/code><\/pre>\n\n\n\n<h4 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"inner_join%E4%B9%9F%E6%98%AF%E5%B0%8F%E8%A1%A8%E6%8B%89%E5%A4%8D%E5%88%B6%E8%A1%A8\"><\/span>inner join\u4e5f\u662f\u5c0f\u8868\u62c9\u590d\u5236\u8868<span class=\"ez-toc-section-end\"><\/span><\/h4>\n\n\n\n<pre class=\"wp-block-code\"><code>gbase> explain select * from t1 inner join t1_2 on t1.name=t1_2.name;\r\n+----+-------------+-------------+-----------+---------------+-----------------+\r\n| ID | MOTION      | OPERATION   | TABLE     | CONDITION     | NO STAT Tab\/Col |\r\n+----+-------------+-------------+-----------+---------------+-----------------+\r\n| 01 | &#91;RESULT]    |  INNER JOIN |           | (name = name) |                 |\r\n|    |             |   Step      | &lt;00>      |               |                 |\r\n|    |             |   Table     | t1&#91;DIS]   |               |                 |\r\n| 00 | &#91;BROADCAST] |  Table      | t1_2&#91;DIS] |               | t1_2            |\r\n+----+-------------+-------------+-----------+---------------+-----------------+\r\n4 rows in set (Elapsed: 00:00:00.57)\r\n<\/code><\/pre>\n\n\n\n<h4 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"right_join_%E5%A4%A7%E8%A1%A8%E6%8B%89%E4%BA%86%E5%A4%8D%E5%88%B6%E8%A1%A8\"><\/span>right join \u5927\u8868\u62c9\u4e86\u590d\u5236\u8868<span class=\"ez-toc-section-end\"><\/span><\/h4>\n\n\n\n<p>\u4ece\u6267\u884c\u8ba1\u5212\u770b\uff0c3300\u4e07\u7684t1\u8868\u88ab\u62c9\u4e86\u590d\u5236\u8868[BROADCAST]\uff0c\u5728\u591a\u6570\u60c5\u51b5\u4e0b\uff0c\u8fd9\u4e2a\u7ed3\u679c\u5e76\u4e0d\u7b26\u5408\u6700\u4f18\u7684\u7ed3\u679c\uff0c\u5c31\u7b97\u662fright\uff0c\u4e5f\u662f\u53ef\u4ee5\u5c0f\u8868\u62c9\u590d\u5236\u8868\u7684\u3002\u540e\u9762\u7684\u4f8b\u5b50\u7ed9\u4e86\u89e3\u51b3\u65b9\u6848\u3002<\/p>\n\n\n\n<ul class=\"wp-block-list\"><li>00\uff1a\u5927\u8868t1\u62c9\u4e86\u590d\u5236\u8868\u3010BROADCAST]<\/li><li>01\uff1a00\u7684\u590d\u5236\u8868\u548ct1_2\u7684\u5c0f\u8868\u505aJOIN,\u5e76\u8fd4\u56de\u7ed3\u679c<\/li><\/ul>\n\n\n\n<pre class=\"wp-block-code\"><code>gbase> explain select * from t1 right join t1_2 on t1.name=t1_2.name;\r\n+----+-------------+------------+-----------+---------------+-----------------+\r\n| ID | MOTION      | OPERATION  | TABLE     | CONDITION     | NO STAT Tab\/Col |\r\n+----+-------------+------------+-----------+---------------+-----------------+\r\n| 01 | &#91;RESULT]    |  LEFT JOIN |           | (name = name) |                 |\r\n|    |             |   Table    | t1_2&#91;DIS] |               |                 |\r\n|    |             |   Step     | &lt;00>      |               |                 |\r\n| 00 | &#91;BROADCAST] |  Table     | t1&#91;DIS]   |               | t1_2            |\r\n+----+-------------+------------+-----------+---------------+-----------------+\r\n4 rows in set (Elapsed: 00:00:00.68)\r\n<\/code><\/pre>\n\n\n\n<h4 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"right_join%E9%80%9A%E8%BF%87%E8%B0%83%E6%95%B4%E5%8F%82%E6%95%B0%EF%BC%8C%E5%A4%A7%E5%B0%8F%E8%A1%A8%E9%83%BD%E5%81%9A%E4%BA%86hash%E9%87%8D%E5%88%86%E5%B8%83\"><\/span>right join\u901a\u8fc7\u8c03\u6574\u53c2\u6570\uff0c\u5927\u5c0f\u8868\u90fd\u505a\u4e86hash\u91cd\u5206\u5e03<span class=\"ez-toc-section-end\"><\/span><\/h4>\n\n\n\n<p>\u901a\u8fc7\u8c03\u6574\u53c2\u6570\uff0c\u88abjoin\u7684\u8868\uff0c\u8d85\u8fc7\u6307\u5b9a\u53c2\u6570\u503c(3300\u4e07\u8d85\u8fc7\u4e861\u4e07\uff09\uff0c\u5219\u88abjoin\u8868\u62c9\u4e86\u5206\u5e03\u8868\uff0c\u800c\u4e0d\u662f\u5206\u5e03\u8868\u3002\u4ece\u672c\u4f8b\u770b\uff0c\u4e3b\u8868\u6ca1\u6709\u62c9\u590d\u5236\u8868\uff0c\u800c\u662f\u5168\u90e8\u62c9\u4e86Hash\u5206\u5e03\u8868\u3002\u53c2\u6570\u542b\u4e49\uff0c\u8bf7\u53c2\u8003  <a href=\"https:\/\/www.gbase8.cn\/3560\">GBase 8a\u6027\u80fd\u4f18\u5316\u6848\u4f8b<\/a><\/p>\n\n\n\n<ul class=\"wp-block-list\"><li>00\uff1a\u5c0f\u8868t1_2\u6839\u636ename\u5217\u505a\u4e86hash\u91cd\u5206\u5e03[REDIST]<\/li><li>01\uff1a\u5927\u8868t1\u6839\u636ename\u5217\u505a\u4e86Hash\u91cd\u5206\u5e03[REDIST]<\/li><li>02\uff1a\u4f7f\u752800\u548c01\u505a\u4e86Hash\u5206\u5e03\u7684\u8868\uff0c\u505a\u672c\u5730join\u5e76\u8fd4\u56de\u7ed3\u679c\u3002<\/li><\/ul>\n\n\n\n<pre class=\"wp-block-code\"><code>gbase> set gcluster_hash_redist_threshold_row=10000;\r\nQuery OK, 0 rows affected (Elapsed: 00:00:00.02)\r\n\r\ngbase> explain select * from t1 right join t1_2 on t1.name=t1_2.name;\r\n+----+----------------+------------+-----------+---------------+-----------------+\r\n| ID | MOTION         | OPERATION  | TABLE     | CONDITION     | NO STAT Tab\/Col |\r\n+----+----------------+------------+-----------+---------------+-----------------+\r\n| 02 | &#91;RESULT]       |  LEFT JOIN |           | (name = name) |                 |\r\n|    |                |   Step     | &lt;00>      |               |                 |\r\n|    |                |   Step     | &lt;01>      |               |                 |\r\n| 01 | &#91;REDIST(name)] |  Table     | t1&#91;DIS]   |               |                 |\r\n| 00 | &#91;REDIST(name)] |  Table     | t1_2&#91;DIS] |               | t1_2            |\r\n+----+----------------+------------+-----------+---------------+-----------------+\r\n5 rows in set (Elapsed: 00:00:00.92)\r\n<\/code><\/pre>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"%E3%80%90%E9%AB%98%E3%80%91%E5%BD%93select%E5%88%97%E7%89%B9%E5%88%AB%E5%A4%9A%E6%97%B6%E7%9A%84%E5%B8%A6limit_%E7%9A%84%E6%8E%92%E5%BA%8F%E4%BC%98%E5%8C%96%E3%80%82\"><\/span>\u3010\u9ad8\u3011\u5f53select\u5217\u7279\u522b\u591a\u65f6\u7684\u5e26limit \u7684\u6392\u5e8f\u4f18\u5316\u3002<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p>\u5982\u679c\u67e5\u8be2\u5217\u975e\u5e38\u591a\uff0c\u8282\u70b9\u4e5f\u591a\uff0c\u7279\u522b\u662foffset\u4e5f\u591a(\u6bd4\u5982\u8282\u70b9\u4e0a\u4e00\u5171100\u4e07\u884c\uff0climit 490000,10 \u8fd9\u79cd\u60c5\u5f62\uff0c\u6bcf\u4e2a\u8282\u70b9\u5c31\u8981\u8fd4\u56de\u63a5\u8fd1\u4e00\u534a\u6570\u636e\u5230\u6c47\u603b\u8282\u70b9)\uff0c\u90a3\u4e48\u5728GATHER\u9636\u6bb5\uff0c\u5c31\u4f1a\u6709\u5927\u91cf\u7684\u6570\u636e\u88ab\u53d1\u9001\u5230\u6c47\u603b\u8282\u70b9\uff0c\u518d\u6b21\u6392\u5e8f\u540e\uff0c\u7edd\u5927\u90e8\u5206\u6570\u636e\u90fd\u5c06\u88ab\u629b\u5f03\uff0c\u9020\u6210\u4e86\u8d44\u6e90\u6d6a\u8d39\u3002\u5728\u8fd9\u79cd\u60c5\u51b5\u4e0b\uff0c\u91c7\u7528\u4e86\u7c7b\u4f3c\u5ef6\u8fdf\u7269\u5316\u7684\u65b9\u5f0f\uff1a\u5148\u628a\u672c\u5730\u6392\u5e8f\u540e\u7684\u5fc5\u987b\u5217\u548c\u884c\u53f7rowid\u53d1\u9001\u5230\u6c47\u603b\u8282\u70b9\uff0c\u5728\u6c47\u603b\u8282\u70b9\u6392\u5e8f\u62ff\u5230\u6700\u7ec8\u7ed3\u679c\u540e\uff0c\u518d\u8fd4\u56de\u539f\u59cb\u8282\u70b9\uff0c\u6309\u7167rowid\u83b7\u5f97\u5176\u5b83\u7684\u5217\uff0c\u8fd9\u6837\u5c31\u51cf\u5c11\u4e86\u6570\u636e\u8d44\u6e90\u7684\u6d6a\u8d39\u3002<\/p>\n\n\n\n<p>\u901a\u8fc7gcluster_order_by_limit_offset_optimize\u53c2\u6570\uff0c\u53ef\u4ee5\u6539\u53d8\u6267\u884c\u8ba1\u5212\u3002\u8bbe\u7f6e\u4e3a1\u5219\u542f\u7528\u5982\u4e0b\u7684\u6267\u884c\u8ba1\u5212\u3002\u9ed8\u8ba4\u662f0\u3002<\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"692\" height=\"263\" src=\"https:\/\/www.gbase8.cn\/wp-content\/uploads\/2021\/02\/image-2.png\" alt=\"GBase 8a\u6267\u884c\u8ba1\u5212 \u5f53select\u5217\u7279\u522b\u591a\u65f6\u7684\u5e26limit \u7684\u6392\u5e8f\u4f18\u5316\" class=\"wp-image-4175\"\/><figcaption>GBase 8a\u6267\u884c\u8ba1\u5212 \u5f53select\u5217\u7279\u522b\u591a\u65f6\u7684\u5e26limit \u7684\u6392\u5e8f\u4f18\u5316<\/figcaption><\/figure>\n\n\n\n<ul class=\"wp-block-list\"><li>00\uff1a\u5c06\u672c\u5730\u6392\u5e8f\u7684\u6570\u636e\uff0c\u653e\u5230\u4e00\u4e2a\u3010\u590d\u5236\u8868 BROADCAST\u3011\u91cc\uff0c\u5176\u4e2d\u5305\u542b\u4e86\u884c\u53f7\u548c\u53c2\u4e0e\u6392\u5e8f\u7684\u5fc5\u987b\u5217\u3002<\/li><li>01\uff1a\u5c06\u590d\u5236\u8868\u6392\u5e8f\uff0c\u62ff\u5230\u7b26\u5408\u8fd4\u56de\u6761\u4ef6\u7684\u7ed3\u679c\u96c6\u3002<\/li><li>02\uff1a\u518d\u5c06\u7b26\u5408\u6761\u4ef6\u7684\u7ed3\u679c\uff0c\u62c9\u6210\u590d\u5236\u8868<\/li><li>03\uff1a\u4ece\u5404\u4e2a\u8282\u70b9\uff0c\u8fd4\u56de\u7b26\u5408\u6761\u4ef6\u7684\u6307\u5b9arowid\u7684\u6240\u8fd4\u56de\u6240\u6709\u5217\u7684\u6570\u636e\u5230\u6c47\u603b\u8282\u70b9\uff0c\u6ce8\u610f\u5176\u4e2d\u7528\u7684\u662f\u5b50\u67e5\u8be2 rowid in<\/li><li>04\uff1a\u5305\u542b\u6240\u6709\u5217\u7684\u8868\u8fdb\u884c\u6392\u5e8f\uff0c\u8fd4\u56de\u7ed3\u679c\u7ed9\u8c03\u7528\u7aef\u3002<\/li><\/ul>\n\n\n\n<pre class=\"wp-block-code\"><code>gbase&gt; set gcluster_order_by_limit_offset_optimize=1;\nQuery OK, 0 rows affected (Elapsed: 00:00:00.00)\n\ngbase&gt; explain select * from t1 order by id  limit 1;\n+----+-------------+-----------+---------+------------------------+-----------------+\n| ID | MOTION      | OPERATION | TABLE   | CONDITION              | NO STAT Tab\/Col |\n+----+-------------+-----------+---------+------------------------+-----------------+\n| 04 | &#91;RESULT]    |  Step     | &lt;03&gt;    |                        |                 |\n|    |             |  ORDER    |         | ORDER BY id ASC        |                 |\n| 03 | &#91;GATHER]    |  SCAN     | t1&#91;DIS] | rowid IN (&#91;SubQuery1]) |                 |\n| 02 | &#91;BROADCAST] |  Step     | &lt;01&gt;    |                        |                 |\n|    |             |  AGG      |         |                        |                 |\n| 01 | &#91;GATHER]    |  Step     | &lt;00&gt;    |                        |                 |\n|    |             |  ORDER    |         | ORDER BY id ASC        |                 |\n|    |             |  LIMIT    |         | LIMIT 1                |                 |\n| 00 | &#91;BROADCAST] |  Table    | t1&#91;DIS] |                        | t1              |\n|    |             |  ORDER    |         | ORDER BY id ASC        |                 |\n|    |             |  LIMIT    |         | LIMIT 1                |                 |\n+----+-------------+-----------+---------+------------------------+-----------------+\n11 rows in set (Elapsed: 00:00:00.02)\n<\/code><\/pre>\n","protected":false},"excerpt":{"rendered":"<p>\u672c\u6587\u9488\u5bf9GBase 8a\u6570\u636e\u5e93\u96c6\u7fa4\u7684\u6267\u884c\u8ba1\u5212\u529f\u80fd(Explain)\uff0c\u91c7\u7528\u4ece\u7b80\u5355\u5230\u590d\u6742\u7684\u5e38\u7528SQL\uff0c\u9010\u6b65\u89e3\u8bfb\u6267\u884c\u8ba1\u5212\u7684\u4f7f\u7528\u65b9\u6cd5\uff0c\u5305\u62ec\u5355\u8868\u805a\u5408group, 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