{"id":78696,"date":"2024-10-16T12:10:16","date_gmt":"2024-10-16T04:10:16","guid":{"rendered":"https:\/\/server.hk\/cnblog\/78696\/"},"modified":"2024-10-16T12:10:16","modified_gmt":"2024-10-16T04:10:16","slug":"mysql%e6%8c%87%e4%bb%a4-ifnull%ef%bc%88%e5%a6%82%e6%9e%9c%e7%82%ba%e7%a9%ba%ef%bc%89","status":"publish","type":"post","link":"https:\/\/server.hk\/cnblog\/78696\/","title":{"rendered":"MySQL\u6307\u4ee4: IFNULL\uff08\u5982\u679c\u70ba\u7a7a\uff09"},"content":{"rendered":"<h1 id=\"mysql%e6%8c%87%e4%bb%a4-ifnull%ef%bc%88%e5%a6%82%e6%9e%9c%e7%82%ba%e7%a9%ba%ef%bc%89-lHlFkEQRcN\">MySQL\u6307\u4ee4: IFNULL\uff08\u5982\u679c\u70ba\u7a7a\uff09<\/h1>\n<p>\u5728\u6578\u64da\u5eab\u7ba1\u7406\u4e2d\uff0c\u8655\u7406\u7a7a\u503c\u662f\u4e00\u500b\u5e38\u898b\u7684\u6311\u6230\u3002MySQL\u63d0\u4f9b\u4e86\u591a\u7a2e\u65b9\u6cd5\u4f86\u8655\u7406\u9019\u4e9b\u7a7a\u503c\uff0c\u5176\u4e2d\u4e4b\u4e00\u5c31\u662fIFNULL\u51fd\u6578\u3002\u9019\u7bc7\u6587\u7ae0\u5c07\u6df1\u5165\u63a2\u8a0eIFNULL\u51fd\u6578\u7684\u7528\u6cd5\u3001\u8a9e\u6cd5\u53ca\u5176\u5728\u5be6\u969b\u61c9\u7528\u4e2d\u7684\u793a\u4f8b\u3002<\/p>\n<h2 id=\"ifnull%e5%87%bd%e6%95%b8%e6%a6%82%e8%bf%b0-lHlFkEQRcN\">IFNULL\u51fd\u6578\u6982\u8ff0<\/h2>\n<p>IFNULL\u51fd\u6578\u662f\u4e00\u500b\u7528\u65bc\u6aa2\u67e5\u67d0\u500b\u8868\u9054\u5f0f\u662f\u5426\u70baNULL\u7684\u51fd\u6578\u3002\u5982\u679c\u8a72\u8868\u9054\u5f0f\u70baNULL\uff0c\u5247\u8fd4\u56de\u6307\u5b9a\u7684\u66ff\u4ee3\u503c\uff1b\u5982\u679c\u4e0d\u662fNULL\uff0c\u5247\u8fd4\u56de\u8a72\u8868\u9054\u5f0f\u7684\u539f\u59cb\u503c\u3002\u9019\u5728\u6578\u64da\u67e5\u8a62\u548c\u5831\u544a\u4e2d\u975e\u5e38\u6709\u7528\uff0c\u56e0\u70ba\u5b83\u53ef\u4ee5\u5e6b\u52a9\u6211\u5011\u907f\u514d\u56e0\u70baNULL\u503c\u800c\u5c0e\u81f4\u7684\u8a08\u7b97\u932f\u8aa4\u6216\u986f\u793a\u554f\u984c\u3002<\/p>\n<h2 id=\"%e8%aa%9e%e6%b3%95-lHlFkEQRcN\">\u8a9e\u6cd5<\/h2>\n<pre><code>IFNULL(expression, alt_value)<\/code><\/pre>\n<ul>\n<li><strong>expression<\/strong>: \u8981\u6aa2\u67e5\u7684\u8868\u9054\u5f0f\u3002<\/li>\n<li><strong>alt_value<\/strong>: \u7576expression\u70baNULL\u6642\u8fd4\u56de\u7684\u66ff\u4ee3\u503c\u3002<\/li>\n<\/ul>\n<h2 id=\"%e4%bd%bf%e7%94%a8%e7%a4%ba%e4%be%8b-lHlFkEQRcN\">\u4f7f\u7528\u793a\u4f8b<\/h2>\n<p>\u4ee5\u4e0b\u662f\u4e00\u4e9b\u4f7f\u7528IFNULL\u51fd\u6578\u7684\u5be6\u969b\u793a\u4f8b\uff0c\u5e6b\u52a9\u60a8\u66f4\u597d\u5730\u7406\u89e3\u5176\u7528\u6cd5\u3002<\/p>\n<h3 id=\"%e7%a4%ba%e4%be%8b1-%e5%9f%ba%e6%9c%ac%e7%94%a8%e6%b3%95-lHlFkEQRcN\">\u793a\u4f8b1: \u57fa\u672c\u7528\u6cd5<\/h3>\n<p>\u5047\u8a2d\u6211\u5011\u6709\u4e00\u500b\u540d\u70ba<code>employees<\/code>\u7684\u8868\uff0c\u8a72\u8868\u5305\u542b\u54e1\u5de5\u7684\u59d3\u540d\u548c\u734e\u91d1\u3002\u67d0\u4e9b\u54e1\u5de5\u7684\u734e\u91d1\u53ef\u80fd\u70baNULL\u3002\u6211\u5011\u53ef\u4ee5\u4f7f\u7528IFNULL\u51fd\u6578\u4f86\u67e5\u8a62\u6240\u6709\u54e1\u5de5\u7684\u734e\u91d1\uff0c\u4e26\u5c07NULL\u503c\u66ff\u63db\u70ba0\u3002<\/p>\n<pre><code>SELECT name, IFNULL(bonus, 0) AS bonus\nFROM employees;<\/code><\/pre>\n<p>\u5728\u9019\u500b\u67e5\u8a62\u4e2d\uff0c\u5982\u679c\u67d0\u4f4d\u54e1\u5de5\u7684\u734e\u91d1\u70baNULL\uff0c\u5247\u67e5\u8a62\u7d50\u679c\u5c07\u986f\u793a0\uff0c\u800c\u4e0d\u662fNULL\u3002<\/p>\n<h3 id=\"%e7%a4%ba%e4%be%8b2-%e7%b5%90%e5%90%88%e5%85%b6%e4%bb%96%e5%87%bd%e6%95%b8%e4%bd%bf%e7%94%a8-lHlFkEQRcN\">\u793a\u4f8b2: \u7d50\u5408\u5176\u4ed6\u51fd\u6578\u4f7f\u7528<\/h3>\n<p>IFNULL\u51fd\u6578\u4e5f\u53ef\u4ee5\u8207\u5176\u4ed6\u51fd\u6578\u7d50\u5408\u4f7f\u7528\u3002\u4f8b\u5982\uff0c\u6211\u5011\u53ef\u4ee5\u8a08\u7b97\u54e1\u5de5\u7684\u7e3d\u6536\u5165\uff08\u57fa\u672c\u5de5\u8cc7\u52a0\u734e\u91d1\uff09\uff0c\u4e26\u5c07NULL\u734e\u91d1\u8996\u70ba0\u3002<\/p>\n<pre><code>SELECT name, salary + IFNULL(bonus, 0) AS total_income\nFROM employees;<\/code><\/pre>\n<p>\u9019\u6a23\uff0c\u6211\u5011\u5c31\u80fd\u5920\u8a08\u7b97\u51fa\u6bcf\u4f4d\u54e1\u5de5\u7684\u7e3d\u6536\u5165\uff0c\u5373\u4f7f\u67d0\u4e9b\u54e1\u5de5\u7684\u734e\u91d1\u70baNULL\u3002<\/p>\n<h3 id=\"%e7%a4%ba%e4%be%8b3-%e5%9c%a8where%e5%ad%90%e5%8f%a5%e4%b8%ad%e4%bd%bf%e7%94%a8-lHlFkEQRcN\">\u793a\u4f8b3: \u5728WHERE\u5b50\u53e5\u4e2d\u4f7f\u7528<\/h3>\n<p>IFNULL\u51fd\u6578\u9084\u53ef\u4ee5\u5728<code>WHERE<\/code>\u5b50\u53e5\u4e2d\u4f7f\u7528\uff0c\u4ee5\u904e\u6ffe\u51fa\u7279\u5b9a\u689d\u4ef6\u7684\u8a18\u9304\u3002\u4f8b\u5982\uff0c\u6211\u5011\u60f3\u67e5\u8a62\u6240\u6709\u734e\u91d1\u4e0d\u70baNULL\u7684\u54e1\u5de5\uff0c\u6216\u8005\u734e\u91d1\u70baNULL\u4f46\u57fa\u672c\u5de5\u8cc7\u5927\u65bc5000\u7684\u54e1\u5de5\u3002<\/p>\n<pre><code>SELECT name\nFROM employees\nWHERE IFNULL(bonus, 0) &gt; 0 OR salary &gt; 5000;<\/code><\/pre>\n<p>\u9019\u6a23\u7684\u67e5\u8a62\u80fd\u5920\u9748\u6d3b\u5730\u8655\u7406NULL\u503c\uff0c\u4e26\u8fd4\u56de\u7b26\u5408\u689d\u4ef6\u7684\u54e1\u5de5\u540d\u55ae\u3002<\/p>\n<h2 id=\"%e7%b8%bd%e7%b5%90-lHlFkEQRcN\">\u7e3d\u7d50<\/h2>\n<p>IFNULL\u51fd\u6578\u5728MySQL\u4e2d\u662f\u4e00\u500b\u975e\u5e38\u5be6\u7528\u7684\u5de5\u5177\uff0c\u80fd\u5920\u6709\u6548\u5730\u8655\u7406\u7a7a\u503c\u554f\u984c\u3002\u901a\u904e\u4f7f\u7528IFNULL\uff0c\u6211\u5011\u53ef\u4ee5\u78ba\u4fdd\u67e5\u8a62\u7d50\u679c\u7684\u5b8c\u6574\u6027\u548c\u6e96\u78ba\u6027\uff0c\u907f\u514d\u56e0NULL\u503c\u800c\u5c0e\u81f4\u7684\u8a08\u7b97\u932f\u8aa4\u3002\u7121\u8ad6\u662f\u5728\u57fa\u672c\u67e5\u8a62\u3001\u8a08\u7b97\u7e3d\u6536\u5165\uff0c\u9084\u662f\u5728\u904e\u6ffe\u689d\u4ef6\u4e2d\uff0cIFNULL\u90fd\u80fd\u63d0\u4f9b\u9748\u6d3b\u7684\u89e3\u6c7a\u65b9\u6848\u3002<\/p>\n<p>\u5982\u679c\u60a8\u6b63\u5728\u5c0b\u627e\u7a69\u5b9a\u4e14\u9ad8\u6548\u7684\u6578\u64da\u5eab\u89e3\u6c7a\u65b9\u6848\uff0c\u8003\u616e\u4f7f\u7528<a href=\"https:\/\/server.hk\">\u9999\u6e2fVPS<\/a>\u4f86\u6258\u7ba1\u60a8\u7684MySQL\u6578\u64da\u5eab\uff0c\u78ba\u4fdd\u60a8\u7684\u61c9\u7528\u7a0b\u5e8f\u80fd\u5920\u9ad8\u6548\u904b\u884c\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"<p>\u4e86\u89e3MySQL\u6307\u4ee4IFNULL\uff0c\u8f15\u9b06\u8655\u7406\u7a7a\u503c\uff0c\u78ba\u4fdd\u67e5\u8a62\u7d50\u679c\u7684\u5b8c\u6574\u6027\u8207\u6e96\u78ba\u6027\u3002\u63d0\u5347\u6578\u64da\u7ba1\u7406\u6548\u7387\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-78696","post","type-post","status-publish","format-standard","hentry","category-database"],"_links":{"self":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/78696","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=78696"}],"version-history":[{"count":1,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/78696\/revisions"}],"predecessor-version":[{"id":78697,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/78696\/revisions\/78697"}],"wp:attachment":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/media?parent=78696"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/categories?post=78696"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/tags?post=78696"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}