<\/span><\/h2>\n\n\n\n\u5982\u4e0b\u662f\u4e00\u4e2a\u83b7\u53d640\u5c81\u4ee5\u4e0b\u4eba\u5458\u6d41\u6c34\u8ba2\u5355\u7684\u4e1a\u52a1\u573a\u666f\u3002\u5176\u4e2did\u662f\u5173\u8054\u6761\u4ef6\uff0c\u800cb.age\u662f\u8fc7\u6ee4\u6761\u4ef6\uff0c\u5206\u522b\u653e\u5728\u4e86on\u548cwhere\u90e8\u5206\u3002<\/p>\n\n\n\n
select a.*,b.age from a join b on a.id=b.id and b.age<40;\nselect a.*,b.age from a join b on a.id=b.id where b.age<40;<\/code><\/pre>\n\n\n\n<\/span>\u6a21\u62df\u6570\u636e<\/span><\/h2>\n\n\n\ngbase> select * from a;\n+------+------+\n| id | bill |\n+------+------+\n| 1 | 100 |\n| 2 | 200 |\n| 1 | 101 |\n| 2 | 202 |\n+------+------+\n4 rows in set (Elapsed: 00:00:00.00)\n\ngbase> select * from b;\n+------+------+\n| id | age |\n+------+------+\n| 1 | 30 |\n| 2 | 50 |\n+------+------+\n2 rows in set (Elapsed: 00:00:00.00)<\/code><\/pre>\n\n\n\n<\/span>\u6267\u884c\u7ed3\u679c<\/span><\/h2>\n\n\n\n\u5206\u522b\u6267\u884c2\u4e2aSQL,\u53ef\u4ee5\u770b\u5230\u7ed3\u679c\u5b8c\u5168\u76f8\u540c\u3002<\/p>\n\n\n\n
gbase> select a.*,b.age from a join b on a.id=b.id and b.age<40;\n+------+------+------+\n| id | bill | age |\n+------+------+------+\n| 1 | 100 | 30 |\n| 1 | 101 | 30 |\n+------+------+------+\n2 rows in set (Elapsed: 00:00:00.03)\n\ngbase> select a.*,b.age from a join b on a.id=b.id where b.age<40\n -> ;\n+------+------+------+\n| id | bill | age |\n+------+------+------+\n| 1 | 100 | 30 |\n| 1 | 101 | 30 |\n+------+------+------+\n2 rows in set (Elapsed: 00:00:00.04)\n<\/code><\/pre>\n\n\n\n<\/span>\u67e5\u770b\u6267\u884c\u8ba1\u5212<\/span><\/h2>\n\n\n\n\u4ece\u6267\u884c\u8ba1\u5212\u770b\uff0c\u4e5f\u662f\u5b8c\u5168\u76f8\u540c\u3002\u90fd\u662f\u5148\u5728B\u8868\u8fc7\u6ee4age<40\u7684\u6570\u636e\uff0c\u7136\u540e\u518d\u548cA\u8868\u505aid=id\u7684join\u3002<\/p>\n\n\n\n
gbase> explain select a.*,b.age from a join b on a.id=b.id and b.age<40;\n+----+-------------+-------------+--------+---------------+-----------------+\n| ID | MOTION | OPERATION | TABLE | CONDITION | NO STAT Tab\/Col |\n+----+-------------+-------------+--------+---------------+-----------------+\n| 01 | [RESULT] | INNER JOIN | | (id = id) | |\n| | | Step | <00> | | |\n| | | Table | a[DIS] | | |\n| 00 | [BROADCAST] | SCAN | b[DIS] | (age{S} < 40) | b |\n+----+-------------+-------------+--------+---------------+-----------------+\n4 rows in set (Elapsed: 00:00:00.01)\n\ngbase> explain select a.*,b.age from a join b on a.id=b.id where b.age<40;\n+----+-------------+-------------+--------+---------------+-----------------+\n| ID | MOTION | OPERATION | TABLE | CONDITION | NO STAT Tab\/Col |\n+----+-------------+-------------+--------+---------------+-----------------+\n| 01 | [RESULT] | INNER JOIN | | (id = id) | |\n| | | Step | <00> | | |\n| | | Table | a[DIS] | | |\n| 00 | [BROADCAST] | SCAN | b[DIS] | (age{S} < 40) | b |\n+----+-------------+-------------+--------+---------------+-----------------+\n4 rows in set (Elapsed: 00:00:00.01)\n\n<\/code><\/pre>\n\n\n\n<\/span>\u96be\u9053where\u548con\u662f\u5b8c\u5168\u4e00\u6837\u7684\u5417\uff1f<\/span><\/h2>\n\n\n\n\u6211\u4eec\u524d\u9762\u505a\u7684\u662finner join, \u6211\u4eec\u6765\u770b\u770b outer join\u7684\u60c5\u51b5\u3002\u4e1a\u52a1SQL\u6539\u9020\u6210 a left join b\u3002<\/p>\n\n\n\n
select a.*,b.age from a left join b on a.id=b.id and b.age<40;\nselect a.*,b.age from a left join b on a.id=b.id where b.age<40;<\/code><\/pre>\n\n\n\n\u518d\u6b21\u8fd0\u884c\u770b\u7ed3\u679c\u3002<\/p>\n\n\n\n
gbase> select a.* from a left join b on a.id=b.id and b.age<40;\n+------+------+\n| id | bill |\ngbase> select a.*,b.age from a left join b on a.id=b.id and b.age<40;\n+------+------+------+\n| id | bill | age |\n+------+------+------+\n| 1 | 100 | 30 |\n| 1 | 101 | 30 |\n| 2 | 200 | NULL |\n| 2 | 202 | NULL |\n+------+------+------+\n4 rows in set (Elapsed: 00:00:00.06)\n<\/code><\/pre>\n\n\n\n\u6ce8\u610f\u5230on\u6761\u4ef6\u7684\u5199\u6cd5\uff0c\u8fd4\u56de\u4e86\u66f4\u591a\u7684\u6570\u636e\uff0c\u5305\u62ec\u90e8\u5206age\u4e3anull\u7684\u3002<\/p>\n\n\n\n
gbase> select a.*,b.age from a left join b on a.id=b.id where b.age<40;\n+------+------+------+\n| id | bill | age |\n+------+------+------+\n| 1 | 100 | 30 |\n| 1 | 101 | 30 |\n+------+------+------+\n2 rows in set (Elapsed: 00:00:00.07)\n<\/code><\/pre>\n\n\n\n\u5199\u5728where\u91cc\u7684\uff0c\u548c\u6700\u5f00\u59cb\u7684\u7ed3\u679c\u662f\u4e00\u6837\u7684\u3002<\/p>\n\n\n\n
\u67e5\u770b\u6267\u884c\u8ba1\u5212\uff0c\u4e5f\u662f\u4e0d\u4e00\u6837\u7684\u3002\u53ef\u4ee5\u770b\u5230where\u65b9\u5f0f\uff0c\u4f1a\u8f6c\u5316\u6210inner join\u8fdb\u884c\u3002\u800con\u90e8\u5206\u7684\uff0c\u5219\u662fleft join\u3002<\/p>\n\n\n\n
gbase> explain select a.*,b.age from a left join b on a.id=b.id and b.age<40;\n+----+-------------+------------+--------+---------------+-----------------+\n| ID | MOTION | OPERATION | TABLE | CONDITION | NO STAT Tab\/Col |\n+----+-------------+------------+--------+---------------+-----------------+\n| 01 | [RESULT] | LEFT JOIN | | (id = id) | |\n| | | Table | a[DIS] | | |\n| | | Step | <00> | | |\n| 00 | [BROADCAST] | SCAN | b[DIS] | (age{S} < 40) | a |\n+----+-------------+------------+--------+---------------+-----------------+\n4 rows in set (Elapsed: 00:00:00.03)\n\ngbase> explain select a.*,b.age from a left join b on a.id=b.id where b.age<40;\n+----+-------------+-------------+--------+---------------+-----------------+\n| ID | MOTION | OPERATION | TABLE | CONDITION | NO STAT Tab\/Col |\n+----+-------------+-------------+--------+---------------+-----------------+\n| 01 | [RESULT] | INNER JOIN | | (id = id) | |\n| | | Step | <00> | | |\n| | | Table | a[DIS] | | |\n| 00 | [BROADCAST] | SCAN | b[DIS] | (age{S} < 40) | b |\n+----+-------------+-------------+--------+---------------+-----------------+\n4 rows in set (Elapsed: 00:00:00.01)\n\n<\/code><\/pre>\n\n\n\n<\/span>\u7ed3\u679c\u4e0d\u4e00\u6837\u7684\u539f\u56e0\u662f\u4ec0\u4e48\uff1f<\/span><\/h2>\n\n\n\n\u533a\u522b\u5728\u4e8e\uff1a<\/p>\n\n\n\n
inner join \u662f\u8ba2\u5355\u5fc5\u987b\u662f40\u5c81\u4e00\u4e0b\u7684\u4eba\u5b8c\u6210\u3002\u5982\u679c\u8be5\u8ba2\u5355\u6ca1\u6709\u627e\u5230\u5bf9\u5e94\u7684\u4eba\uff0c\u6216\u8005\u5bf9\u5e94\u7684\u4eba\u5e74\u9f84\u4e0d\u5c0f\u4e8e40\u5c81\uff0c\u5219\u4e0d\u7b26\u5408\u8981\u6c42\u3002<\/p>\n\n\n\n
left join \u662f\u4ee5\u8ba2\u5355a\u8868\u4e3a\u51c6\uff0c\u53bb\u67e5\u8be2\u7b26\u5408\u6761\u4ef6\uff08\u5c0f\u4e8e40\u5c81\uff09\u7684\u4eba\u5458\u7684\u4fe1\u606f\uff0c\u5982\u679c\u67e5\u4e0d\u5230\u6216\u8005\u4e0d\u7b26\u5408\u8981\u6c42\u5c31\u8fd4\u56denull\u3002<\/p>\n\n\n\n
<\/span>\u7ed3\u8bba<\/span><\/h2>\n\n\n\n\u5bf9\u4e8einner join, \u8fc7\u6ee4\u6761\u4ef6\u5199\u5728on\u91cc\u548cwhere\u91cc\u6ca1\u6709\u533a\u522b\u3002
\u5bf9\u4e8eouter join, \u8fc7\u6ee4\u6761\u4ef6\u5199\u5728on\u91cc\u548cwhere\u91cc\u662f\u6709\u533a\u522b\u7684\u3002<\/p>\n\n\n\n
\u5b9e\u9645\u4e1a\u52a1\uff0c\u9700\u8981\u8c28\u614e\u7684\u6839\u636e\u9700\u6c42\uff0c\u786e\u8ba4\u6761\u4ef6\u7684\u4f4d\u7f6e\uff0c\u907f\u514d\u7ed3\u679c\u4e0e\u9884\u671f\u4e0d\u7b26\u3002<\/p>\n\n\n\n
<\/p>","protected":false},"excerpt":{"rendered":"
\u6211\u4eec\u7ecf\u5e38\u9047\u5230\u7684\u4e00\u4e2a\u95ee\u9898\u5c31\u662f\uff0c\u90fd\u662f\u8fc7\u6ee4\u6761\u4ef6\uff0c\u6ce8\u610f\u4e0d\u662fjoin\u5217\uff0c\u653e\u5728where\u91cc\u548con\u91cc\u6709\u5565\u533a\u522b\u5462\uff1f\u672c\u6587\u4ee5GBase\u6570\u636e\u5e93\u4e3a\u4f8b\uff0c\u7814\u7a76\u4e0b\u672c\u95ee\u9898\u3002<\/p>","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[4],"tags":[81],"class_list":["post-3072","post","type-post","status-publish","format-standard","hentry","category-gbase8a","tag-81"],"_links":{"self":[{"href":"https:\/\/www.gbase8.cn\/en\/wp-json\/wp\/v2\/posts\/3072","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.gbase8.cn\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.gbase8.cn\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.gbase8.cn\/en\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.gbase8.cn\/en\/wp-json\/wp\/v2\/comments?post=3072"}],"version-history":[{"count":6,"href":"https:\/\/www.gbase8.cn\/en\/wp-json\/wp\/v2\/posts\/3072\/revisions"}],"predecessor-version":[{"id":8085,"href":"https:\/\/www.gbase8.cn\/en\/wp-json\/wp\/v2\/posts\/3072\/revisions\/8085"}],"wp:attachment":[{"href":"https:\/\/www.gbase8.cn\/en\/wp-json\/wp\/v2\/media?parent=3072"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.gbase8.cn\/en\/wp-json\/wp\/v2\/categories?post=3072"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.gbase8.cn\/en\/wp-json\/wp\/v2\/tags?post=3072"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}