{"id":143835,"date":"2024-11-01T01:39:18","date_gmt":"2024-10-31T17:39:18","guid":{"rendered":"https:\/\/server.hk\/cnblog\/143835\/"},"modified":"2024-11-01T01:39:19","modified_gmt":"2024-10-31T17:39:19","slug":"sql-%e6%8a%80%e5%b7%a7%ef%bc%9a%e5%a6%82%e4%bd%95%e5%b0%8d%e6%95%b8%e6%93%9a%e5%ba%ab%e4%b8%ad%e6%9f%90%e4%b8%80%e5%88%97%e9%80%b2%e8%a1%8c%e5%8e%bb%e9%87%8d%e6%9f%a5%e8%a9%a2%ef%bc%9f-sql-%e6%9f%a5","status":"publish","type":"post","link":"https:\/\/server.hk\/cnblog\/143835\/","title":{"rendered":"SQL \u6280\u5de7\uff1a\u5982\u4f55\u5c0d\u6578\u64da\u5eab\u4e2d\u67d0\u4e00\u5217\u9032\u884c\u53bb\u91cd\u67e5\u8a62\uff1f (sql \u67e5\u8a62\u67d0\u4e00\u5217\u53bb\u91cd\u6578\u64da\u5eab)"},"content":{"rendered":"<h1 id=\"sql-%e6%8a%80%e5%b7%a7%ef%bc%9a%e5%a6%82%e4%bd%95%e5%b0%8d%e6%95%b8%e6%93%9a%e5%ba%ab%e4%b8%ad%e6%9f%90%e4%b8%80%e5%88%97%e9%80%b2%e8%a1%8c%e5%8e%bb%e9%87%8d%e6%9f%a5%e8%a9%a2%ef%bc%9f-pjsxwNsoeA\">SQL \u6280\u5de7\uff1a\u5982\u4f55\u5c0d\u6578\u64da\u5eab\u4e2d\u67d0\u4e00\u5217\u9032\u884c\u53bb\u91cd\u67e5\u8a62\uff1f<\/h1>\n<p>\u5728\u6578\u64da\u5eab\u7ba1\u7406\u4e2d\uff0c\u53bb\u91cd\u67e5\u8a62\u662f\u4e00\u500b\u5e38\u898b\u7684\u9700\u6c42\uff0c\u5c24\u5176\u662f\u5728\u8655\u7406\u5927\u91cf\u6578\u64da\u6642\u3002\u53bb\u91cd\u67e5\u8a62\u7684\u76ee\u7684\u662f\u5f9e\u6578\u64da\u5eab\u4e2d\u63d0\u53d6\u552f\u4e00\u7684\u6578\u64da\uff0c\u907f\u514d\u91cd\u8907\u7684\u8a18\u9304\u3002\u672c\u6587\u5c07\u4ecb\u7d39\u5982\u4f55\u4f7f\u7528 SQL \u8a9e\u53e5\u5c0d\u6578\u64da\u5eab\u4e2d\u7684\u67d0\u4e00\u5217\u9032\u884c\u53bb\u91cd\u67e5\u8a62\uff0c\u4e26\u63d0\u4f9b\u76f8\u95dc\u7684\u793a\u4f8b\u548c\u6280\u5de7\u3002<\/p>\n<h2 id=\"%e4%bb%80%e9%ba%bc%e6%98%af%e5%8e%bb%e9%87%8d%e6%9f%a5%e8%a9%a2%ef%bc%9f-pjsxwNsoeA\">\u4ec0\u9ebc\u662f\u53bb\u91cd\u67e5\u8a62\uff1f<\/h2>\n<p>\u53bb\u91cd\u67e5\u8a62\u662f\u6307\u5f9e\u6578\u64da\u5eab\u4e2d\u9078\u53d6\u552f\u4e00\u7684\u8a18\u9304\uff0c\u901a\u5e38\u662f\u91dd\u5c0d\u67d0\u4e00\u7279\u5b9a\u7684\u5217\u9032\u884c\u64cd\u4f5c\u3002\u9019\u5728\u6578\u64da\u5206\u6790\u548c\u5831\u544a\u4e2d\u975e\u5e38\u91cd\u8981\uff0c\u56e0\u70ba\u91cd\u8907\u7684\u6578\u64da\u53ef\u80fd\u6703\u5c0e\u81f4\u932f\u8aa4\u7684\u7d50\u8ad6\u6216\u4e0d\u6e96\u78ba\u7684\u5831\u544a\u3002<\/p>\n<h2 id=\"%e4%bd%bf%e7%94%a8-distinct-%e9%97%9c%e9%8d%b5%e5%ad%97-pjsxwNsoeA\">\u4f7f\u7528 DISTINCT \u95dc\u9375\u5b57<\/h2>\n<p>\u5728 SQL \u4e2d\uff0c\u6700\u5e38\u7528\u7684\u53bb\u91cd\u67e5\u8a62\u65b9\u6cd5\u662f\u4f7f\u7528 <code>DISTINCT<\/code> \u95dc\u9375\u5b57\u3002\u9019\u500b\u95dc\u9375\u5b57\u53ef\u4ee5\u7528\u4f86\u9078\u53d6\u67d0\u4e00\u5217\u7684\u552f\u4e00\u503c\u3002\u4ee5\u4e0b\u662f\u57fa\u672c\u7684\u8a9e\u6cd5\uff1a<\/p>\n<pre><code>SELECT DISTINCT column_name FROM table_name;<\/code><\/pre>\n<p>\u4f8b\u5982\uff0c\u5047\u8a2d\u6211\u5011\u6709\u4e00\u500b\u540d\u70ba <code>employees<\/code> \u7684\u8868\u683c\uff0c\u5176\u4e2d\u5305\u542b\u54e1\u5de5\u7684\u59d3\u540d\u548c\u90e8\u9580\u3002\u5982\u679c\u6211\u5011\u60f3\u8981\u7372\u53d6\u6240\u6709\u552f\u4e00\u7684\u90e8\u9580\u540d\u7a31\uff0c\u53ef\u4ee5\u4f7f\u7528\u4ee5\u4e0b\u67e5\u8a62\uff1a<\/p>\n<pre><code>SELECT DISTINCT department FROM employees;<\/code><\/pre>\n<h2 id=\"%e4%bd%bf%e7%94%a8-group-by-%e5%ad%90%e5%8f%a5-pjsxwNsoeA\">\u4f7f\u7528 GROUP BY \u5b50\u53e5<\/h2>\n<p>\u9664\u4e86 <code>DISTINCT<\/code>\uff0c\u53e6\u4e00\u7a2e\u5e38\u7528\u7684\u53bb\u91cd\u65b9\u6cd5\u662f\u4f7f\u7528 <code>GROUP BY<\/code> \u5b50\u53e5\u3002\u9019\u500b\u5b50\u53e5\u53ef\u4ee5\u5c07\u7d50\u679c\u96c6\u6309\u6307\u5b9a\u7684\u5217\u9032\u884c\u5206\u7d44\uff0c\u4e26\u4e14\u53ef\u4ee5\u8207\u805a\u5408\u51fd\u6578\u4e00\u8d77\u4f7f\u7528\u3002\u4ee5\u4e0b\u662f\u57fa\u672c\u7684\u8a9e\u6cd5\uff1a<\/p>\n<pre><code>SELECT column_name, COUNT(*) FROM table_name GROUP BY column_name;<\/code><\/pre>\n<p>\u4f8b\u5982\uff0c\u5982\u679c\u6211\u5011\u60f3\u8981\u7372\u53d6\u6bcf\u500b\u90e8\u9580\u7684\u54e1\u5de5\u6578\u91cf\uff0c\u53ef\u4ee5\u4f7f\u7528\u4ee5\u4e0b\u67e5\u8a62\uff1a<\/p>\n<pre><code>SELECT department, COUNT(*) FROM employees GROUP BY department;<\/code><\/pre>\n<h2 id=\"%e4%bd%bf%e7%94%a8%e5%ad%90%e6%9f%a5%e8%a9%a2-pjsxwNsoeA\">\u4f7f\u7528\u5b50\u67e5\u8a62<\/h2>\n<p>\u5728\u67d0\u4e9b\u60c5\u6cc1\u4e0b\uff0c\u60a8\u53ef\u80fd\u9700\u8981\u4f7f\u7528\u5b50\u67e5\u8a62\u4f86\u7372\u53d6\u552f\u4e00\u503c\u3002\u9019\u7a2e\u65b9\u6cd5\u901a\u5e38\u7528\u65bc\u66f4\u8907\u96dc\u7684\u67e5\u8a62\u4e2d\u3002\u4ee5\u4e0b\u662f\u57fa\u672c\u7684\u8a9e\u6cd5\uff1a<\/p>\n<pre><code>SELECT column_name FROM (SELECT DISTINCT column_name FROM table_name) AS temp;<\/code><\/pre>\n<p>\u4f8b\u5982\uff0c\u5982\u679c\u6211\u5011\u60f3\u8981\u7372\u53d6\u6240\u6709\u552f\u4e00\u7684\u90e8\u9580\u540d\u7a31\uff0c\u4f46\u540c\u6642\u9700\u8981\u5176\u4ed6\u76f8\u95dc\u4fe1\u606f\uff0c\u53ef\u4ee5\u4f7f\u7528\u5b50\u67e5\u8a62\uff1a<\/p>\n<pre><code>SELECT * FROM (SELECT DISTINCT department FROM employees) AS unique_departments;<\/code><\/pre>\n<h2 id=\"%e6%b3%a8%e6%84%8f%e4%ba%8b%e9%a0%85-pjsxwNsoeA\">\u6ce8\u610f\u4e8b\u9805<\/h2>\n<ul>\n<li>\u4f7f\u7528 <code>DISTINCT<\/code> \u6703\u5f71\u97ff\u67e5\u8a62\u6027\u80fd\uff0c\u7279\u5225\u662f\u5728\u8655\u7406\u5927\u91cf\u6578\u64da\u6642\uff0c\u56e0\u6b64\u61c9\u8b39\u614e\u4f7f\u7528\u3002<\/li>\n<li>\u5728\u4f7f\u7528 <code>GROUP BY<\/code> \u6642\uff0c\u78ba\u4fdd\u6240\u6709\u975e\u805a\u5408\u5217\u90fd\u5305\u542b\u5728 <code>GROUP BY<\/code> \u5b50\u53e5\u4e2d\u3002<\/li>\n<li>\u5b50\u67e5\u8a62\u53ef\u80fd\u6703\u589e\u52a0\u67e5\u8a62\u7684\u8907\u96dc\u6027\uff0c\u61c9\u6839\u64da\u5be6\u969b\u9700\u6c42\u9078\u64c7\u5408\u9069\u7684\u65b9\u6cd5\u3002<\/li>\n<\/ul>\n<h2 id=\"%e7%b8%bd%e7%b5%90-pjsxwNsoeA\">\u7e3d\u7d50<\/h2>\n<p>\u53bb\u91cd\u67e5\u8a62\u662f\u6578\u64da\u5eab\u64cd\u4f5c\u4e2d\u4e00\u500b\u91cd\u8981\u7684\u6280\u5de7\uff0c\u80fd\u5920\u5e6b\u52a9\u7528\u6236\u7372\u53d6\u552f\u4e00\u7684\u6578\u64da\u3002\u7121\u8ad6\u662f\u4f7f\u7528 <code>DISTINCT<\/code>\u3001<code>GROUP BY<\/code> \u9084\u662f\u5b50\u67e5\u8a62\uff0c\u9078\u64c7\u5408\u9069\u7684\u65b9\u6cd5\u53ef\u4ee5\u63d0\u9ad8\u67e5\u8a62\u6548\u7387\u548c\u6e96\u78ba\u6027\u3002\u5c0d\u65bc\u9700\u8981\u8655\u7406\u5927\u91cf\u6578\u64da\u7684\u7528\u6236\uff0c\u9078\u64c7\u5408\u9069\u7684 <a href=\"https:\/\/server.hk\">VPS<\/a> \u65b9\u6848\u53ef\u4ee5\u63d0\u4f9b\u66f4\u597d\u7684\u6027\u80fd\u548c\u7a69\u5b9a\u6027\uff0c\u8b93\u6578\u64da\u5eab\u64cd\u4f5c\u66f4\u52a0\u6d41\u66a2\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"<p>\u5b78\u7fd2\u5982\u4f55\u5728 SQL \u4e2d\u5c0d\u6578\u64da\u5eab\u67d0\u4e00\u5217\u9032\u884c\u53bb\u91cd\u67e5\u8a62\uff0c\u63d0\u5347\u6578\u64da\u8655\u7406\u6548\u7387\uff0c\u7c21\u5316\u6578\u64da\u5206\u6790\u904e\u7a0b\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-143835","post","type-post","status-publish","format-standard","hentry","category-database"],"_links":{"self":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/143835","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=143835"}],"version-history":[{"count":1,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/143835\/revisions"}],"predecessor-version":[{"id":143836,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/143835\/revisions\/143836"}],"wp:attachment":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/media?parent=143835"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/categories?post=143835"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/tags?post=143835"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}