{"id":79330,"date":"2024-10-16T12:56:25","date_gmt":"2024-10-16T04:56:25","guid":{"rendered":"https:\/\/server.hk\/cnblog\/79330\/"},"modified":"2024-10-16T12:56:26","modified_gmt":"2024-10-16T04:56:26","slug":"mysql%e6%8c%87%e4%bb%a4-nullif%ef%bc%88%e5%a6%82%e6%9e%9c%e7%9b%b8%e7%ad%89%e8%bf%94%e5%9b%9e%e7%a9%ba%ef%bc%8c%e5%90%a6%e5%89%87%e8%bf%94%e5%9b%9e%e7%ac%ac%e4%b8%80%e5%80%8b%e8%a1%a8%e9%81%94","status":"publish","type":"post","link":"https:\/\/server.hk\/cnblog\/79330\/","title":{"rendered":"MySQL\u6307\u4ee4: NULLIF\uff08\u5982\u679c\u76f8\u7b49\u8fd4\u56de\u7a7a\uff0c\u5426\u5247\u8fd4\u56de\u7b2c\u4e00\u500b\u8868\u9054\u5f0f\u7684\u503c\uff09"},"content":{"rendered":"<h1 id=\"mysql%e6%8c%87%e4%bb%a4-nullif%ef%bc%88%e5%a6%82%e6%9e%9c%e7%9b%b8%e7%ad%89%e8%bf%94%e5%9b%9e%e7%a9%ba%ef%bc%8c%e5%90%a6%e5%89%87%e8%bf%94%e5%9b%9e%e7%ac%ac%e4%b8%80%e5%80%8b%e8%a1%a8%e9%81%94-IeAtDFkAxb\">MySQL\u6307\u4ee4: NULLIF\uff08\u5982\u679c\u76f8\u7b49\u8fd4\u56de\u7a7a\uff0c\u5426\u5247\u8fd4\u56de\u7b2c\u4e00\u500b\u8868\u9054\u5f0f\u7684\u503c\uff09<\/h1>\n<p>\u5728\u6578\u64da\u5eab\u7ba1\u7406\u4e2d\uff0cMySQL\u662f\u4e00\u500b\u5ee3\u6cdb\u4f7f\u7528\u7684\u95dc\u806f\u6578\u64da\u5eab\u7ba1\u7406\u7cfb\u7d71\u3002\u5b83\u63d0\u4f9b\u4e86\u591a\u7a2e\u529f\u80fd\u5f37\u5927\u7684\u6307\u4ee4\u4f86\u8655\u7406\u6578\u64da\uff0c\u5176\u4e2d\u4e4b\u4e00\u5c31\u662fNULLIF\u51fd\u6578\u3002NULLIF\u51fd\u6578\u7684\u4e3b\u8981\u4f5c\u7528\u662f\u6bd4\u8f03\u5169\u500b\u8868\u9054\u5f0f\uff0c\u5982\u679c\u5b83\u5011\u76f8\u7b49\uff0c\u5247\u8fd4\u56deNULL\uff1b\u5982\u679c\u4e0d\u76f8\u7b49\uff0c\u5247\u8fd4\u56de\u7b2c\u4e00\u500b\u8868\u9054\u5f0f\u7684\u503c\u3002\u9019\u4e00\u7279\u6027\u5728\u6578\u64da\u8655\u7406\u548c\u67e5\u8a62\u4e2d\u975e\u5e38\u6709\u7528\uff0c\u7279\u5225\u662f\u5728\u9700\u8981\u907f\u514d\u67d0\u4e9b\u7279\u5b9a\u503c\u7684\u60c5\u6cc1\u4e0b\u3002<\/p>\n<h2 id=\"nullif%e5%87%bd%e6%95%b8%e7%9a%84%e8%aa%9e%e6%b3%95-IeAtDFkAxb\">NULLIF\u51fd\u6578\u7684\u8a9e\u6cd5<\/h2>\n<p>NULLIF\u51fd\u6578\u7684\u57fa\u672c\u8a9e\u6cd5\u5982\u4e0b\uff1a<\/p>\n<pre><code>NULLIF(expr1, expr2)<\/code><\/pre>\n<p>\u5728\u9019\u88e1\uff0c<code>expr1<\/code>\u548c<code>expr2<\/code>\u662f\u8981\u9032\u884c\u6bd4\u8f03\u7684\u5169\u500b\u8868\u9054\u5f0f\u3002\u5982\u679c<code>expr1<\/code>\u7b49\u65bc<code>expr2<\/code>\uff0c\u5247\u8fd4\u56deNULL\uff1b\u5426\u5247\u8fd4\u56de<code>expr1<\/code>\u7684\u503c\u3002<\/p>\n<h2 id=\"nullif%e7%9a%84%e4%bd%bf%e7%94%a8%e5%a0%b4%e6%99%af-IeAtDFkAxb\">NULLIF\u7684\u4f7f\u7528\u5834\u666f<\/h2>\n<p>NULLIF\u51fd\u6578\u5728\u591a\u7a2e\u60c5\u6cc1\u4e0b\u90fd\u975e\u5e38\u6709\u7528\uff0c\u4ee5\u4e0b\u662f\u4e00\u4e9b\u5e38\u898b\u7684\u4f7f\u7528\u5834\u666f\uff1a<\/p>\n<ul>\n<li><strong>\u907f\u514d\u96f6\u503c\uff1a<\/strong>\u5728\u8a08\u7b97\u6bd4\u7387\u6216\u767e\u5206\u6bd4\u6642\uff0c\u901a\u5e38\u9700\u8981\u907f\u514d\u9664\u4ee5\u96f6\u7684\u60c5\u6cc1\u3002\u4f7f\u7528NULLIF\u53ef\u4ee5\u6709\u6548\u5730\u8655\u7406\u9019\u7a2e\u60c5\u6cc1\u3002<\/li>\n<li><strong>\u6578\u64da\u6e05\u7406\uff1a<\/strong>\u5728\u6578\u64da\u6e05\u7406\u904e\u7a0b\u4e2d\uff0cNULLIF\u53ef\u4ee5\u7528\u4f86\u5c07\u67d0\u4e9b\u4e0d\u9700\u8981\u7684\u503c\uff08\u5982\u7a7a\u5b57\u7b26\u4e32\u6216\u7279\u5b9a\u7684\u6a19\u8a18\u503c\uff09\u8f49\u63db\u70baNULL\u3002<\/li>\n<li><strong>\u689d\u4ef6\u67e5\u8a62\uff1a<\/strong>\u5728\u67e5\u8a62\u4e2d\uff0cNULLIF\u53ef\u4ee5\u7528\u4f86\u6839\u64da\u7279\u5b9a\u689d\u4ef6\u8fd4\u56de\u4e0d\u540c\u7684\u7d50\u679c\uff0c\u5f9e\u800c\u63d0\u9ad8\u67e5\u8a62\u7684\u9748\u6d3b\u6027\u3002<\/li>\n<\/ul>\n<h2 id=\"%e5%af%a6%e9%9a%9b%e7%af%84%e4%be%8b-IeAtDFkAxb\">\u5be6\u969b\u7bc4\u4f8b<\/h2>\n<p>\u4ee5\u4e0b\u662f\u4e00\u500b\u4f7f\u7528NULLIF\u7684\u5be6\u969b\u7bc4\u4f8b\uff0c\u5047\u8a2d\u6211\u5011\u6709\u4e00\u500b\u540d\u70ba<code>sales<\/code>\u7684\u8868\uff0c\u5305\u542b<code>product_id<\/code>\u548c<code>quantity_sold<\/code>\u5169\u500b\u5b57\u6bb5\uff1a<\/p>\n<pre><code>SELECT product_id, \n       NULLIF(quantity_sold, 0) AS adjusted_quantity\nFROM sales;<\/code><\/pre>\n<p>\u5728\u9019\u500b\u67e5\u8a62\u4e2d\uff0c\u5982\u679c<code>quantity_sold<\/code>\u7684\u503c\u70ba0\uff0c\u5247<code>adjusted_quantity<\/code>\u5c07\u8fd4\u56deNULL\uff1b\u5426\u5247\uff0c\u5b83\u5c07\u8fd4\u56de<code>quantity_sold<\/code>\u7684\u503c\u3002\u9019\u6a23\u53ef\u4ee5\u907f\u514d\u5728\u5f8c\u7e8c\u8a08\u7b97\u4e2d\u51fa\u73fe\u96f6\u503c\u7684\u554f\u984c\u3002<\/p>\n<h2 id=\"%e7%b5%90%e5%90%88%e5%85%b6%e4%bb%96%e5%87%bd%e6%95%b8%e4%bd%bf%e7%94%a8-IeAtDFkAxb\">\u7d50\u5408\u5176\u4ed6\u51fd\u6578\u4f7f\u7528<\/h2>\n<p>NULLIF\u51fd\u6578\u4e5f\u53ef\u4ee5\u8207\u5176\u4ed6MySQL\u51fd\u6578\u7d50\u5408\u4f7f\u7528\uff0c\u4ee5\u5be6\u73fe\u66f4\u8907\u96dc\u7684\u908f\u8f2f\u3002\u4f8b\u5982\uff0c\u60a8\u53ef\u4ee5\u5c07NULLIF\u8207COALESCE\u51fd\u6578\u7d50\u5408\u4f7f\u7528\uff0c\u9019\u6a23\u53ef\u4ee5\u5728NULL\u7684\u60c5\u6cc1\u4e0b\u63d0\u4f9b\u4e00\u500b\u9ed8\u8a8d\u503c\uff1a<\/p>\n<pre><code>SELECT product_id, \n       COALESCE(NULLIF(quantity_sold, 0), 'No Sales') AS sales_info\nFROM sales;<\/code><\/pre>\n<p>\u5728\u9019\u500b\u67e5\u8a62\u4e2d\uff0c\u5982\u679c<code>quantity_sold<\/code>\u70ba0\uff0c\u5247<code>sales_info<\/code>\u5c07\u986f\u793a&#8217;No Sales&#8217;\uff0c\u800c\u4e0d\u662fNULL\uff0c\u9019\u6a23\u53ef\u4ee5\u4f7f\u7d50\u679c\u66f4\u52a0\u6613\u65bc\u7406\u89e3\u3002<\/p>\n<h2 id=\"%e7%b8%bd%e7%b5%90-IeAtDFkAxb\">\u7e3d\u7d50<\/h2>\n<p>NULLIF\u51fd\u6578\u5728MySQL\u4e2d\u662f\u4e00\u500b\u975e\u5e38\u5be6\u7528\u7684\u5de5\u5177\uff0c\u80fd\u5920\u5e6b\u52a9\u958b\u767c\u8005\u5728\u6578\u64da\u8655\u7406\u904e\u7a0b\u4e2d\u6709\u6548\u5730\u7ba1\u7406\u548c\u6e05\u7406\u6578\u64da\u3002\u901a\u904e\u4f7f\u7528NULLIF\uff0c\u60a8\u53ef\u4ee5\u907f\u514d\u4e0d\u5fc5\u8981\u7684\u932f\u8aa4\uff0c\u4e26\u63d0\u9ad8\u67e5\u8a62\u7684\u9748\u6d3b\u6027\u548c\u53ef\u8b80\u6027\u3002\u5c0d\u65bc\u9700\u8981\u8655\u7406\u5927\u91cf\u6578\u64da\u7684\u61c9\u7528\u7a0b\u5e8f\u4f86\u8aaa\uff0c\u9019\u4e00\u51fd\u6578\u7121\u7591\u662f\u4e0d\u53ef\u6216\u7f3a\u7684\u3002<\/p>\n<p>\u5982\u679c\u60a8\u6b63\u5728\u5c0b\u627e\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\u9019\u5c07\u70ba\u60a8\u7684\u61c9\u7528\u7a0b\u5e8f\u63d0\u4f9b\u7a69\u5b9a\u548c\u53ef\u9760\u7684\u652f\u6301\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"<p>\u4e86\u89e3MySQL\u6307\u4ee4NULLIF\uff1a\u7576\u5169\u500b\u8868\u9054\u5f0f\u76f8\u7b49\u6642\u8fd4\u56deNULL\uff0c\u5426\u5247\u8fd4\u56de\u7b2c\u4e00\u500b\u8868\u9054\u5f0f\u7684\u503c\uff0c\u7c21\u5316\u6578\u64da\u8655\u7406\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-79330","post","type-post","status-publish","format-standard","hentry","category-database"],"_links":{"self":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/79330","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=79330"}],"version-history":[{"count":1,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/79330\/revisions"}],"predecessor-version":[{"id":79331,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/79330\/revisions\/79331"}],"wp:attachment":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/media?parent=79330"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/categories?post=79330"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/tags?post=79330"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}