{"id":5946,"date":"2021-05-13T15:10:02","date_gmt":"2021-05-13T07:10:02","guid":{"rendered":"https:\/\/www.gbase8.cn\/?p=5946"},"modified":"2021-05-18T10:43:41","modified_gmt":"2021-05-18T02:43:41","slug":"clickhouse-lowcardinality-%e6%95%b0%e6%8d%ae%e7%b1%bb%e5%9e%8b%e7%9a%84%e7%94%a8%e6%b3%95%e6%a0%b7%e4%be%8b","status":"publish","type":"post","link":"https:\/\/www.gbase8.cn\/en\/5946","title":{"rendered":"Clickhouse LowCardinality \u6570\u636e\u7c7b\u578b\u7684\u7528\u6cd5\u6837\u4f8b"},"content":{"rendered":"<p>ClickHouse\u7684\u6570\u636e\u7c7b\u578b\u4e2d\uff0cLowCardinality \u7528\u4e8e\u5904\u7406\u91cd\u590d\u5ea6\u9ad8\u7684\u6570\u503c\uff0c\u7279\u522b\u662f\u5bf9\u4e8e\u6bd4\u8f83\u957f\u7684\u5b57\u7b26\u4e32\u7c7b\u578b\u3002<\/p>\n\n\n\n<div id=\"ez-toc-container\" class=\"ez-toc-v2_0_84 counter-hierarchy ez-toc-counter ez-toc-grey ez-toc-container-direction\">\n<p class=\"ez-toc-title\" style=\"cursor:inherit\">Directory Navigation<\/p>\n<label for=\"ez-toc-cssicon-toggle-item-6a2b2c900e42b\" class=\"ez-toc-cssicon-toggle-label\"><span class=\"\"><span class=\"eztoc-hide\" style=\"display:none;\">Toggle<\/span><span class=\"ez-toc-icon-toggle-span\"><svg style=\"fill: #999;color:#999\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" class=\"list-377408\" width=\"20px\" height=\"20px\" viewbox=\"0 0 24 24\" fill=\"none\"><path d=\"M6 6H4v2h2V6zm14 0H8v2h12V6zM4 11h2v2H4v-2zm16 0H8v2h12v-2zM4 16h2v2H4v-2zm16 0H8v2h12v-2z\" fill=\"currentColor\"><\/path><\/svg><svg style=\"fill: #999;color:#999\" class=\"arrow-unsorted-368013\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"10px\" height=\"10px\" viewbox=\"0 0 24 24\" version=\"1.2\" baseprofile=\"tiny\"><path d=\"M18.2 9.3l-6.2-6.3-6.2 6.3c-.2.2-.3.4-.3.7s.1.5.3.7c.2.2.4.3.7.3h11c.3 0 .5-.1.7-.3.2-.2.3-.5.3-.7s-.1-.5-.3-.7zM5.8 14.7l6.2 6.3 6.2-6.3c.2-.2.3-.5.3-.7s-.1-.5-.3-.7c-.2-.2-.4-.3-.7-.3h-11c-.3 0-.5.1-.7.3-.2.2-.3.5-.3.7s.1.5.3.7z\"\/><\/svg><\/span><\/span><\/label><input type=\"checkbox\"  id=\"ez-toc-cssicon-toggle-item-6a2b2c900e42b\"  aria-label=\"Toggle\" \/><nav><ul class='ez-toc-list ez-toc-list-level-1' ><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-1\" href=\"https:\/\/www.gbase8.cn\/en\/5946\/#%E8%AF%AD%E6%B3%95\" >\u8bed\u6cd5<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-2\" href=\"https:\/\/www.gbase8.cn\/en\/5946\/#%E8%AF%B4%E6%98%8E\" >\u8bf4\u660e<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-3\" href=\"https:\/\/www.gbase8.cn\/en\/5946\/#%E6%A0%B7%E4%BE%8B\" >\u6837\u4f8b<\/a><\/li><\/ul><\/nav><\/div>\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"%E8%AF%AD%E6%B3%95\"><\/span>\u8bed\u6cd5<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<pre class=\"wp-block-code\"><code>LowCardinality(data_type)<\/code><\/pre>\n\n\n\n<p><code>data_type<\/code>\u00a0\u2014\u00a0<a href=\"https:\/\/clickhouse.tech\/docs\/en\/sql-reference\/data-types\/string\/\">String<\/a>,\u00a0<a href=\"https:\/\/clickhouse.tech\/docs\/en\/sql-reference\/data-types\/fixedstring\/\">FixedString<\/a>,\u00a0<a href=\"https:\/\/clickhouse.tech\/docs\/en\/sql-reference\/data-types\/date\/\">Date<\/a>,\u00a0<a href=\"https:\/\/clickhouse.tech\/docs\/en\/sql-reference\/data-types\/datetime\/\">DateTime<\/a>, \u548c\u6570\u5b57\u7c7b\u578b\uff0c\u9664\u4e86<a href=\"https:\/\/clickhouse.tech\/docs\/en\/sql-reference\/data-types\/decimal\/\">Decimal<\/a><code>\u3002<\/code><\/p>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"%E8%AF%B4%E6%98%8E\"><\/span>\u8bf4\u660e<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p><code>LowCardinality<\/code>\u00a0\u4fee\u6539\u4e86\u6570\u636e\u5904\u7406\u8fc7\u7a0b\u4e2d\u7684\u6570\u636e\u5b58\u50a8\u65b9\u6cd5\u548c\u89c4\u5219\uff0c\u4f7f\u7528\u5b57\u5178\u7f16\u7801(Directionary coding)\u65b9\u6848\uff0c\u53ef\u4ee5\u663e\u8457\u7684\u63d0\u9ad8SELECT\u6027\u80fd\u3002<\/p>\n\n\n\n<p>\u63d0\u5347\u6548\u679c\u4e0e\u6570\u636e\u7279\u6027\u6709\u5173\u3002\u5982\u679c\u5b57\u5178\u91cc\u5305\u542b\u4e0d\u8d85\u8fc71\u4e07\u4e2a\u4e0d\u540c\u7684\u503c\uff0c\u5219\u53ef\u4ee5\u660e\u663e\u7684\u63d0\u9ad8\u6570\u636e\u8bfb\u53d6\u548c\u5b58\u50a8\u6027\u80fd\u3002\u5982\u679c\u8d85\u8fc7\u4e8610\u4e07\u4e2a\u552f\u4e00\u7684\u503c\uff0c\u53ef\u80fd\u6027\u80fd\u8fd8\u4e0d\u5982\u666e\u901a\u7684\u6570\u636e\u7c7b\u578b\u3002 <\/p>\n\n\n\n<p>\u8fd9\u4e2a\u9700\u8981\u6d4b\u8bd5\uff0c\u7279\u522b\u662f\u552f\u4e00\u503c\u5728\u603b\u6570\u636e\u91cf\u7684\u6bd4\u4f8b\uff0c\u4f46\u6570\u636e\u8d8a\u5bbd\uff0c\u552f\u4e00\u503c\u8d8a\u5c11\uff0c\u6548\u679c\u80af\u5b9a\u8d8a\u597d\u3002\u50cf\u56fd\u5bb6\uff0c\u5730\u533a\u8fd9\u7c7b\u975e\u5e38\u6709\u9650\u7684\u6570\u503c\uff0c\u5219\u603b\u662f\u4f1a\u6709\u6548\u679c\u7684\u3002\u800c\u5bf9\u624b\u673a\u53f7\uff0cIP\u8fd9\u7c7b\u975e\u5e38\u5206\u6563\u7684\uff0c\u5219\u6548\u679c\u65e0\u6cd5\u4fdd\u969c\u3002<\/p>\n\n\n\n<p>\u5f53\u4f7f\u7528\u5b57\u7b26\u7c7b\u578b\u7684\u65f6\u5019\uff0c\u53ef\u4ee5\u8003\u8651\u4f7f\u7528\u00a0<code>LowCardinality<\/code>\u00a0\u4ee3\u66ff<a href=\"https:\/\/clickhouse.tech\/docs\/zh\/sql-reference\/data-types\/enum\/\">Enum<\/a>\u3002\u00a0<code>LowCardinality<\/code>\u00a0\u901a\u5e38\u66f4\u52a0\u7075\u6d3b\u548c\u9ad8\u6548\u3002<\/p>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"%E6%A0%B7%E4%BE%8B\"><\/span>\u6837\u4f8b<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p>\u5982\u4e0b\u7684\u5c18\u4e16\uff0c\u6c11\u65cf\uff0c\u5730\u533a\u3001\u8d85\u5e02\u5730\u6bb5\u7b49\uff0c\u90fd\u662f\u53ef\u4ee5\u7528\u8fd9\u4e2a\u7c7b\u578b\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>CREATE TABLE customer\r\n(\r\n        C_CUSTKEY       UInt32,\r\n        C_NAME          String,\r\n        C_ADDRESS       String,\r\n        C_CITY          LowCardinality(String),\r\n        C_NATION        LowCardinality(String),\r\n        C_REGION        LowCardinality(String),\r\n        C_PHONE         String,\r\n        C_MKTSEGMENT    LowCardinality(String)\r\n)\r\nENGINE = MergeTree ORDER BY (C_CUSTKEY);<\/code><\/pre>\n\n\n\n<p><\/p>","protected":false},"excerpt":{"rendered":"<p>ClickHouse\u7684\u6570\u636e\u7c7b\u578b\u4e2d\uff0cLowCardinality \u7528\u4e8e\u5904\u7406\u91cd\u590d\u5ea6\u9ad8\u7684\u6570\u503c\uff0c\u7279\u522b\u662f\u5bf9\u4e8e\u6bd4\u8f83\u957f\u7684\u5b57\u7b26\u4e32\u7c7b\u578b\u3002<\/p>","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[86],"tags":[],"class_list":["post-5946","post","type-post","status-publish","format-standard","hentry","category-clickhouse"],"_links":{"self":[{"href":"https:\/\/www.gbase8.cn\/en\/wp-json\/wp\/v2\/posts\/5946","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=5946"}],"version-history":[{"count":5,"href":"https:\/\/www.gbase8.cn\/en\/wp-json\/wp\/v2\/posts\/5946\/revisions"}],"predecessor-version":[{"id":5954,"href":"https:\/\/www.gbase8.cn\/en\/wp-json\/wp\/v2\/posts\/5946\/revisions\/5954"}],"wp:attachment":[{"href":"https:\/\/www.gbase8.cn\/en\/wp-json\/wp\/v2\/media?parent=5946"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.gbase8.cn\/en\/wp-json\/wp\/v2\/categories?post=5946"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.gbase8.cn\/en\/wp-json\/wp\/v2\/tags?post=5946"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}