{"id":196223,"date":"2024-11-13T21:30:34","date_gmt":"2024-11-13T13:30:34","guid":{"rendered":"https:\/\/server.hk\/cnblog\/196223\/"},"modified":"2024-11-13T21:30:36","modified_gmt":"2024-11-13T13:30:36","slug":"%e6%8e%8c%e6%8f%a1%e6%95%b8%e6%93%9a%e5%ba%ab%e4%b8%adcase%e7%9a%84%e9%9d%88%e6%b4%bb%e9%81%8b%e7%94%a8%e6%8a%80%e5%b7%a7-%e6%95%b8%e6%93%9a%e5%ba%ab-case%e7%9a%84%e7%94%a8%e6%b3%95","status":"publish","type":"post","link":"https:\/\/server.hk\/cnblog\/196223\/","title":{"rendered":"\u638c\u63e1\u6578\u64da\u5eab\u4e2dCASE\u7684\u9748\u6d3b\u904b\u7528\u6280\u5de7 (\u6578\u64da\u5eab case\u7684\u7528\u6cd5)"},"content":{"rendered":"<h1 id=\"%e6%8e%8c%e6%8f%a1%e6%95%b8%e6%93%9a%e5%ba%ab%e4%b8%adcase%e7%9a%84%e9%9d%88%e6%b4%bb%e9%81%8b%e7%94%a8%e6%8a%80%e5%b7%a7-%e6%95%b8%e6%93%9a%e5%ba%ab-case-%e7%9a%84%e7%94%a8%e6%b3%95-JmGMioLLJu\">\u638c\u63e1\u6578\u64da\u5eab\u4e2dCASE\u7684\u9748\u6d3b\u904b\u7528\u6280\u5de7 (\u6578\u64da\u5eab CASE \u7684\u7528\u6cd5)<\/h1>\n<p>\u5728\u6578\u64da\u5eab\u7ba1\u7406\u7cfb\u7d71\u4e2d\uff0cCASE\u8a9e\u53e5\u662f\u4e00\u500b\u975e\u5e38\u5f37\u5927\u7684\u5de5\u5177\uff0c\u80fd\u5920\u5e6b\u52a9\u958b\u767c\u8005\u5728\u67e5\u8a62\u4e2d\u9032\u884c\u689d\u4ef6\u5224\u65b7\u548c\u6578\u64da\u8f49\u63db\u3002\u7121\u8ad6\u662f\u5728SQL\u67e5\u8a62\u4e2d\u9032\u884c\u6578\u64da\u5206\u985e\uff0c\u9084\u662f\u5728\u5831\u544a\u4e2d\u751f\u6210\u52d5\u614b\u5167\u5bb9\uff0cCASE\u8a9e\u53e5\u90fd\u80fd\u63d0\u4f9b\u9748\u6d3b\u7684\u89e3\u6c7a\u65b9\u6848\u3002\u672c\u6587\u5c07\u6df1\u5165\u63a2\u8a0eCASE\u8a9e\u53e5\u7684\u7528\u6cd5\u53ca\u5176\u5728\u6578\u64da\u5eab\u4e2d\u7684\u9748\u6d3b\u904b\u7528\u6280\u5de7\u3002<\/p>\n<h2 id=\"%e4%bb%80%e9%ba%bc%e6%98%afcase%e8%aa%9e%e5%8f%a5%ef%bc%9f-JmGMioLLJu\">\u4ec0\u9ebc\u662fCASE\u8a9e\u53e5\uff1f<\/h2>\n<p>CASE\u8a9e\u53e5\u662f\u4e00\u7a2e\u689d\u4ef6\u8868\u9054\u5f0f\uff0c\u5141\u8a31\u7528\u6236\u5728SQL\u67e5\u8a62\u4e2d\u6839\u64da\u7279\u5b9a\u689d\u4ef6\u8fd4\u56de\u4e0d\u540c\u7684\u503c\u3002\u5b83\u7684\u57fa\u672c\u8a9e\u6cd5\u5982\u4e0b\uff1a<\/p>\n<pre><code>CASE\n    WHEN condition1 THEN result1\n    WHEN condition2 THEN result2\n    ...\n    ELSE resultN\nEND<\/code><\/pre>\n<p>\u5728\u9019\u6bb5\u8a9e\u6cd5\u4e2d\uff0c\u7576\u6eff\u8db3\u67d0\u500b\u689d\u4ef6\u6642\uff0cCASE\u8a9e\u53e5\u5c07\u8fd4\u56de\u5c0d\u61c9\u7684\u7d50\u679c\u3002\u5982\u679c\u6c92\u6709\u4efb\u4f55\u689d\u4ef6\u6eff\u8db3\uff0c\u5247\u8fd4\u56deELSE\u90e8\u5206\u7684\u7d50\u679c\uff08\u5982\u679c\u6709\u5b9a\u7fa9\u7684\u8a71\uff09\u3002<\/p>\n<h2 id=\"case%e8%aa%9e%e5%8f%a5%e7%9a%84%e5%9f%ba%e6%9c%ac%e7%94%a8%e6%b3%95-JmGMioLLJu\">CASE\u8a9e\u53e5\u7684\u57fa\u672c\u7528\u6cd5<\/h2>\n<p>CASE\u8a9e\u53e5\u53ef\u4ee5\u7528\u65bcSELECT\u3001UPDATE\u3001DELETE\u7b49\u591a\u7a2eSQL\u8a9e\u53e5\u4e2d\u3002\u4ee5\u4e0b\u662f\u4e00\u4e9b\u5e38\u898b\u7684\u7528\u6cd5\u793a\u4f8b\uff1a<\/p>\n<h3 id=\"1-%e5%9c%a8select%e8%aa%9e%e5%8f%a5%e4%b8%ad%e4%bd%bf%e7%94%a8case-JmGMioLLJu\">1. \u5728SELECT\u8a9e\u53e5\u4e2d\u4f7f\u7528CASE<\/h3>\n<p>\u5728\u67e5\u8a62\u4e2d\u4f7f\u7528CASE\u8a9e\u53e5\uff0c\u53ef\u4ee5\u6839\u64da\u4e0d\u540c\u7684\u689d\u4ef6\u8fd4\u56de\u4e0d\u540c\u7684\u503c\u3002\u4f8b\u5982\uff0c\u5047\u8a2d\u6211\u5011\u6709\u4e00\u500b\u54e1\u5de5\u8868\uff0c\u60f3\u8981\u6839\u64da\u54e1\u5de5\u7684\u85aa\u6c34\u7bc4\u570d\u4f86\u5206\u985e\u54e1\u5de5\uff1a<\/p>\n<pre><code>SELECT employee_id,\n       salary,\n       CASE\n           WHEN salary &lt; 30000 THEN &#039;\u4f4e\u85aa&#039;\n           WHEN salary BETWEEN 30000 AND 60000 THEN &#039;\u4e2d\u85aa&#039;\n           ELSE &#039;\u9ad8\u85aa&#039;\n       END AS salary_category\nFROM employees;<\/code><\/pre>\n<p>\u9019\u6bb5\u67e5\u8a62\u5c07\u6839\u64da\u85aa\u6c34\u7684\u4e0d\u540c\u7bc4\u570d\uff0c\u70ba\u6bcf\u4f4d\u54e1\u5de5\u5206\u914d\u4e00\u500b\u85aa\u6c34\u985e\u5225\u3002<\/p>\n<h3 id=\"2-%e5%9c%a8update%e8%aa%9e%e5%8f%a5%e4%b8%ad%e4%bd%bf%e7%94%a8case-JmGMioLLJu\">2. \u5728UPDATE\u8a9e\u53e5\u4e2d\u4f7f\u7528CASE<\/h3>\n<p>CASE\u8a9e\u53e5\u4e5f\u53ef\u4ee5\u7528\u65bcUPDATE\u64cd\u4f5c\u4e2d\uff0c\u6839\u64da\u4e0d\u540c\u7684\u689d\u4ef6\u66f4\u65b0\u4e0d\u540c\u7684\u503c\u3002\u4f8b\u5982\uff1a<\/p>\n<pre><code>UPDATE employees\nSET salary = CASE\n                 WHEN salary &lt; 30000 THEN salary * 1.1\n                 WHEN salary BETWEEN 30000 AND 60000 THEN salary * 1.05\n                 ELSE salary * 1.02\n             END;<\/code><\/pre>\n<p>\u9019\u6bb5\u4ee3\u78bc\u5c07\u6839\u64da\u54e1\u5de5\u7684\u85aa\u6c34\u7bc4\u570d\uff0c\u5c0d\u5176\u85aa\u6c34\u9032\u884c\u4e0d\u540c\u7684\u8abf\u6574\u3002<\/p>\n<h2 id=\"case%e8%aa%9e%e5%8f%a5%e7%9a%84%e9%80%b2%e9%9a%8e%e7%94%a8%e6%b3%95-JmGMioLLJu\">CASE\u8a9e\u53e5\u7684\u9032\u968e\u7528\u6cd5<\/h2>\n<p>\u9664\u4e86\u57fa\u672c\u7684\u7528\u6cd5\uff0cCASE\u8a9e\u53e5\u9084\u53ef\u4ee5\u8207\u5176\u4ed6SQL\u51fd\u6578\u7d50\u5408\u4f7f\u7528\uff0c\u9032\u4e00\u6b65\u589e\u5f37\u5176\u9748\u6d3b\u6027\u3002\u4f8b\u5982\uff0c\u8207\u805a\u5408\u51fd\u6578\u7d50\u5408\u4f7f\u7528\uff1a<\/p>\n<pre><code>SELECT department_id,\n       COUNT(CASE WHEN salary  60000 THEN 1 END) AS high_salary_count\nFROM employees\nGROUP BY department_id;<\/code><\/pre>\n<p>\u9019\u6bb5\u67e5\u8a62\u5c07\u8a08\u7b97\u6bcf\u500b\u90e8\u9580\u4e2d\u4e0d\u540c\u85aa\u6c34\u7bc4\u570d\u7684\u54e1\u5de5\u6578\u91cf\uff0c\u63d0\u4f9b\u4e86\u66f4\u6df1\u5165\u7684\u6578\u64da\u5206\u6790\u80fd\u529b\u3002<\/p>\n<h2 id=\"%e4%bd%bf%e7%94%a8case%e8%aa%9e%e5%8f%a5%e7%9a%84%e6%b3%a8%e6%84%8f%e4%ba%8b%e9%a0%85-JmGMioLLJu\">\u4f7f\u7528CASE\u8a9e\u53e5\u7684\u6ce8\u610f\u4e8b\u9805<\/h2>\n<ul>\n<li><strong>\u6027\u80fd\u8003\u91cf\uff1a<\/strong>\u5728\u8655\u7406\u5927\u91cf\u6578\u64da\u6642\uff0c\u904e\u591a\u7684CASE\u8a9e\u53e5\u53ef\u80fd\u6703\u5f71\u97ff\u67e5\u8a62\u6027\u80fd\uff0c\u56e0\u6b64\u61c9\u8b39\u614e\u4f7f\u7528\u3002<\/li>\n<li><strong>\u53ef\u8b80\u6027\uff1a<\/strong>\u904e\u65bc\u8907\u96dc\u7684CASE\u8a9e\u53e5\u53ef\u80fd\u6703\u964d\u4f4eSQL\u67e5\u8a62\u7684\u53ef\u8b80\u6027\uff0c\u5efa\u8b70\u9069\u7576\u5206\u89e3\u67e5\u8a62\u3002<\/li>\n<li><strong>\u6578\u64da\u985e\u578b\u4e00\u81f4\u6027\uff1a<\/strong>CASE\u8a9e\u53e5\u7684\u8fd4\u56de\u503c\u5fc5\u9808\u662f\u76f8\u540c\u6578\u64da\u985e\u578b\uff0c\u5426\u5247\u6703\u5c0e\u81f4\u932f\u8aa4\u3002<\/li>\n<\/ul>\n<h2 id=\"%e7%b8%bd%e7%b5%90-JmGMioLLJu\">\u7e3d\u7d50<\/h2>\n<p>CASE\u8a9e\u53e5\u5728\u6578\u64da\u5eab\u67e5\u8a62\u4e2d\u63d0\u4f9b\u4e86\u9748\u6d3b\u7684\u689d\u4ef6\u5224\u65b7\u80fd\u529b\uff0c\u80fd\u5920\u5e6b\u52a9\u958b\u767c\u8005\u6839\u64da\u4e0d\u540c\u7684\u9700\u6c42\u9032\u884c\u6578\u64da\u8655\u7406\u548c\u5206\u6790\u3002\u7121\u8ad6\u662f\u5728SELECT\u9084\u662fUPDATE\u64cd\u4f5c\u4e2d\uff0cCASE\u8a9e\u53e5\u90fd\u80fd\u6709\u6548\u63d0\u5347\u67e5\u8a62\u7684\u9748\u6d3b\u6027\u548c\u53ef\u8b80\u6027\u3002\u638c\u63e1CASE\u8a9e\u53e5\u7684\u7528\u6cd5\uff0c\u5c07\u6709\u52a9\u65bc\u958b\u767c\u8005\u5728\u6578\u64da\u5eab\u7ba1\u7406\u4e2d\u66f4\u9ad8\u6548\u5730\u8655\u7406\u6578\u64da\u3002<\/p>\n<p>\u5982\u679c\u60a8\u5c0d\u65bc\u6578\u64da\u5eab\u7ba1\u7406\u6216\u5176\u4ed6\u6280\u8853\u554f\u984c\u6709\u8208\u8da3\uff0c\u6b61\u8fce\u8a2a\u554f\u6211\u5011\u7684\u7db2\u7ad9\u4e86\u89e3\u66f4\u591a\u8cc7\u8a0a\uff0c\u7279\u5225\u662f\u6211\u5011\u7684<a 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