{"id":173199,"date":"2024-11-07T16:00:23","date_gmt":"2024-11-07T08:00:23","guid":{"rendered":"https:\/\/server.hk\/cnblog\/173199\/"},"modified":"2024-11-07T16:00:23","modified_gmt":"2024-11-07T08:00:23","slug":"%e5%a6%82%e4%bd%95%e8%99%95%e7%90%86%e6%95%b8%e6%93%9a%e5%ba%ab%e4%b8%ad%e7%9a%84distinct%e7%a9%ba%e5%80%bc%e5%95%8f%e9%a1%8c%ef%bc%9f-%e6%95%b8%e6%93%9a%e5%ba%abdistinct-%e7%a9%ba%e5%80%bc","status":"publish","type":"post","link":"https:\/\/server.hk\/cnblog\/173199\/","title":{"rendered":"\u5982\u4f55\u8655\u7406\u6578\u64da\u5eab\u4e2d\u7684distinct\u7a7a\u503c\u554f\u984c\uff1f (\u6578\u64da\u5eabdistinct \u7a7a\u503c)"},"content":{"rendered":"<h1 id=\"%e5%a6%82%e4%bd%95%e8%99%95%e7%90%86%e6%95%b8%e6%93%9a%e5%ba%ab%e4%b8%ad%e7%9a%84distinct%e7%a9%ba%e5%80%bc%e5%95%8f%e9%a1%8c%ef%bc%9f-%e6%95%b8%e6%93%9a%e5%ba%abdistinct-%e7%a9%ba%e5%80%bc-HUmDgMJDKf\">\u5982\u4f55\u8655\u7406\u6578\u64da\u5eab\u4e2d\u7684distinct\u7a7a\u503c\u554f\u984c\uff1f (\u6578\u64da\u5eabdistinct \u7a7a\u503c)<\/h1>\n<p>\u5728\u6578\u64da\u5eab\u7ba1\u7406\u4e2d\uff0c\u7a7a\u503c\uff08NULL\uff09\u662f\u4e00\u500b\u5e38\u898b\u7684\u6982\u5ff5\uff0c\u4ee3\u8868\u8457\u7f3a\u5931\u6216\u672a\u77e5\u7684\u6578\u64da\u3002\u5728\u4f7f\u7528 SQL \u67e5\u8a62\u6642\uff0c\u5c24\u5176\u662f\u5728\u4f7f\u7528 <code>DISTINCT<\/code> \u95dc\u9375\u5b57\u6642\uff0c\u7a7a\u503c\u7684\u8655\u7406\u53ef\u80fd\u6703\u5f15\u767c\u4e00\u4e9b\u554f\u984c\u3002\u672c\u6587\u5c07\u63a2\u8a0e\u5982\u4f55\u6709\u6548\u5730\u8655\u7406\u6578\u64da\u5eab\u4e2d\u7684 <code>DISTINCT<\/code> \u7a7a\u503c\u554f\u984c\uff0c\u4e26\u63d0\u4f9b\u4e00\u4e9b\u5be6\u7528\u7684\u793a\u4f8b\u548c\u89e3\u6c7a\u65b9\u6848\u3002<\/p>\n<h2 id=\"%e7%90%86%e8%a7%a3%e7%a9%ba%e5%80%bc%e7%9a%84%e6%a6%82%e5%bf%b5-HUmDgMJDKf\">\u7406\u89e3\u7a7a\u503c\u7684\u6982\u5ff5<\/h2>\n<p>\u5728 SQL \u4e2d\uff0c\u7a7a\u503c\uff08NULL\uff09\u4e26\u4e0d\u7b49\u540c\u65bc\u96f6\u6216\u7a7a\u5b57\u7b26\u4e32\u3002\u5b83\u8868\u793a\u4e00\u500b\u7f3a\u5931\u7684\u503c\uff0c\u9019\u610f\u5473\u8457\u8a72\u5b57\u6bb5\u7684\u6578\u64da\u672a\u77e5\u6216\u4e0d\u9069\u7528\u3002\u7576\u6211\u5011\u5728\u67e5\u8a62\u4e2d\u4f7f\u7528 <code>DISTINCT<\/code> \u6642\uff0c\u6578\u64da\u5eab\u6703\u5ffd\u7565\u6240\u6709\u7684\u7a7a\u503c\uff0c\u9019\u53ef\u80fd\u6703\u5c0e\u81f4\u4e00\u4e9b\u610f\u60f3\u4e0d\u5230\u7684\u7d50\u679c\u3002<\/p>\n<h2 id=\"distinct-%e7%9a%84%e5%9f%ba%e6%9c%ac%e7%94%a8%e6%b3%95-HUmDgMJDKf\">DISTINCT \u7684\u57fa\u672c\u7528\u6cd5<\/h2>\n<p><code>DISTINCT<\/code> \u95dc\u9375\u5b57\u7528\u65bc\u9078\u64c7\u552f\u4e00\u7684\u6578\u64da\u884c\u3002\u4ee5\u4e0b\u662f\u4e00\u500b\u57fa\u672c\u7684\u793a\u4f8b\uff1a<\/p>\n<pre><code>SELECT DISTINCT column_name FROM table_name;<\/code><\/pre>\n<p>\u9019\u689d\u67e5\u8a62\u5c07\u8fd4\u56de <code>table_name<\/code> \u4e2d <code>column_name<\/code> \u7684\u6240\u6709\u552f\u4e00\u503c\uff0c\u4f46\u6703\u5ffd\u7565\u7a7a\u503c\u3002<\/p>\n<h2 id=\"%e7%a9%ba%e5%80%bc%e7%9a%84%e5%bd%b1%e9%9f%bf-HUmDgMJDKf\">\u7a7a\u503c\u7684\u5f71\u97ff<\/h2>\n<p>\u7576\u6578\u64da\u5eab\u4e2d\u5b58\u5728\u7a7a\u503c\u6642\uff0c\u4f7f\u7528 <code>DISTINCT<\/code> \u53ef\u80fd\u6703\u5c0e\u81f4\u7d50\u679c\u4e0d\u5982\u9810\u671f\u3002\u4f8b\u5982\uff0c\u8003\u616e\u4ee5\u4e0b\u6578\u64da\uff1a<\/p>\n<pre><code>+------------+\n| column_name|\n+------------+\n| A          |\n| B          |\n| NULL       |\n| A          |\n| NULL       |\n| C          |\n+------------+<\/code><\/pre>\n<p>\u57f7\u884c\u4ee5\u4e0b\u67e5\u8a62\uff1a<\/p>\n<pre><code>SELECT DISTINCT column_name FROM table_name;<\/code><\/pre>\n<p>\u7d50\u679c\u5c07\u662f\uff1a<\/p>\n<pre><code>+------------+\n| column_name|\n+------------+\n| A          |\n| B          |\n| C          |\n+------------+<\/code><\/pre>\n<p>\u5982\u4e0a\u6240\u793a\uff0c\u7a7a\u503c\u88ab\u5ffd\u7565\u4e86\uff0c\u9019\u53ef\u80fd\u6703\u5c0e\u81f4\u5c0d\u6578\u64da\u7684\u8aa4\u89e3\u3002<\/p>\n<h2 id=\"%e8%99%95%e7%90%86%e7%a9%ba%e5%80%bc%e7%9a%84%e7%ad%96%e7%95%a5-HUmDgMJDKf\">\u8655\u7406\u7a7a\u503c\u7684\u7b56\u7565<\/h2>\n<p>\u70ba\u4e86\u66f4\u597d\u5730\u8655\u7406\u7a7a\u503c\u554f\u984c\uff0c\u53ef\u4ee5\u8003\u616e\u4ee5\u4e0b\u5e7e\u7a2e\u7b56\u7565\uff1a<\/p>\n<ul>\n<li><strong>\u4f7f\u7528 COALESCE \u51fd\u6578\uff1a<\/strong>\u9019\u500b\u51fd\u6578\u53ef\u4ee5\u5c07\u7a7a\u503c\u66ff\u63db\u70ba\u5176\u4ed6\u503c\u3002\u4f8b\u5982\uff1a<\/li>\n<pre><code>SELECT DISTINCT COALESCE(column_name, 'Unknown') AS column_name FROM table_name;<\/code><\/pre>\n<li><strong>\u4f7f\u7528 CASE \u8a9e\u53e5\uff1a<\/strong>\u9019\u53ef\u4ee5\u8b93\u4f60\u66f4\u9748\u6d3b\u5730\u8655\u7406\u7a7a\u503c\u3002\u4f8b\u5982\uff1a<\/li>\n<pre><code>SELECT DISTINCT CASE WHEN column_name IS NULL THEN 'Unknown' ELSE column_name END AS column_name FROM table_name;<\/code><\/pre>\n<li><strong>\u904e\u6ffe\u7a7a\u503c\uff1a<\/strong>\u5728\u67e5\u8a62\u4e2d\u76f4\u63a5\u904e\u6ffe\u6389\u7a7a\u503c\uff1a<\/li>\n<pre><code>SELECT DISTINCT column_name FROM table_name WHERE column_name IS NOT NULL;<\/code><\/pre>\n<\/ul>\n<h2 id=\"%e5%af%a6%e9%9a%9b%e6%87%89%e7%94%a8%e7%a4%ba%e4%be%8b-HUmDgMJDKf\">\u5be6\u969b\u61c9\u7528\u793a\u4f8b<\/h2>\n<p>\u5047\u8a2d\u6211\u5011\u6709\u4e00\u500b\u7528\u6236\u8868\uff0c\u5305\u542b\u7528\u6236\u7684\u59d3\u540d\u548c\u96fb\u5b50\u90f5\u4ef6\u5730\u5740\uff0c\u5176\u4e2d\u4e00\u4e9b\u96fb\u5b50\u90f5\u4ef6\u5730\u5740\u70ba\u7a7a\u3002\u4ee5\u4e0b\u662f\u5982\u4f55\u4f7f\u7528\u4e0a\u8ff0\u65b9\u6cd5\u4f86\u7372\u53d6\u552f\u4e00\u7684\u96fb\u5b50\u90f5\u4ef6\u5730\u5740\uff1a<\/p>\n<pre><code>SELECT DISTINCT COALESCE(email, 'No Email') AS email FROM users;<\/code><\/pre>\n<p>\u9019\u6a23\uff0c\u6211\u5011\u5c31\u80fd\u5920\u7372\u5f97\u6240\u6709\u552f\u4e00\u7684\u96fb\u5b50\u90f5\u4ef6\u5730\u5740\uff0c\u4e26\u5c07\u7a7a\u503c\u66ff\u63db\u70ba &#8216;No Email&#8217;\u3002<\/p>\n<h2 id=\"%e7%b8%bd%e7%b5%90-HUmDgMJDKf\">\u7e3d\u7d50<\/h2>\n<p>\u5728\u6578\u64da\u5eab\u4e2d\u8655\u7406 <code>DISTINCT<\/code> \u7a7a\u503c\u554f\u984c\u662f\u6578\u64da\u7ba1\u7406\u4e2d\u7684\u4e00\u500b\u91cd\u8981\u8ab2\u984c\u3002\u901a\u904e\u7406\u89e3\u7a7a\u503c\u7684\u6982\u5ff5\u53ca\u5176\u5c0d\u67e5\u8a62\u7d50\u679c\u7684\u5f71\u97ff\uff0c\u6211\u5011\u53ef\u4ee5\u63a1\u53d6\u9069\u7576\u7684\u7b56\u7565\u4f86\u8655\u7406\u9019\u4e9b\u7a7a\u503c\u3002\u7121\u8ad6\u662f\u4f7f\u7528 <code>COALESCE<\/code> \u51fd\u6578\u3001<code>CASE<\/code> \u8a9e\u53e5\uff0c\u9084\u662f\u76f4\u63a5\u904e\u6ffe\u7a7a\u503c\uff0c\u9019\u4e9b\u65b9\u6cd5\u90fd\u80fd\u5e6b\u52a9\u6211\u5011\u7372\u5f97\u66f4\u6e96\u78ba\u7684\u6578\u64da\u7d50\u679c\u3002<\/p>\n<p>\u5982\u679c\u60a8\u6b63\u5728\u5c0b\u627e\u9ad8\u6548\u7684 <a href=\"https:\/\/server.hk\">\u9999\u6e2fVPS<\/a> \u89e3\u6c7a\u65b9\u6848\uff0cServer.HK \u63d0\u4f9b\u591a\u7a2e\u9078\u64c7\uff0c\u5e6b\u52a9\u60a8\u8f15\u9b06\u7ba1\u7406\u6578\u64da\u5eab\u548c\u61c9\u7528\u7a0b\u5e8f\u3002\u7121\u8ad6\u662f <a href=\"https:\/\/server.hk\">\u9999\u6e2f\u4f3a\u670d\u5668<\/a> \u9084\u662f <a href=\"https:\/\/server.hk\">\u96f2\u4f3a\u670d\u5668<\/a>\uff0c\u6211\u5011\u90fd\u80fd\u6eff\u8db3\u60a8\u7684\u9700\u6c42\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"<p>\u4e86\u89e3\u5982\u4f55\u5728\u6578\u64da\u5eab\u4e2d\u6709\u6548\u8655\u7406distinct\u7a7a\u503c\u554f\u984c\uff0c\u78ba\u4fdd\u67e5\u8a62\u7d50\u679c\u7684\u6e96\u78ba\u6027\u8207\u5b8c\u6574\u6027\u3002<\/p>\n","protected":false},"author":0,"featured_media":0,"comment_status":"closed","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[101],"tags":[],"class_list":["post-173199","post","type-post","status-publish","format-standard","hentry","category-database"],"_links":{"self":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/173199","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/types\/post"}],"replies":[{"embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/comments?post=173199"}],"version-history":[{"count":1,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/173199\/revisions"}],"predecessor-version":[{"id":173200,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/173199\/revisions\/173200"}],"wp:attachment":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/media?parent=173199"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/categories?post=173199"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/tags?post=173199"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}