{"id":77918,"date":"2024-10-16T11:19:15","date_gmt":"2024-10-16T03:19:15","guid":{"rendered":"https:\/\/server.hk\/cnblog\/77918\/"},"modified":"2024-10-16T11:19:16","modified_gmt":"2024-10-16T03:19:16","slug":"mysql%e6%8c%87%e4%bb%a4-coalesce%ef%bc%88%e8%bf%94%e5%9b%9e%e7%ac%ac%e4%b8%80%e5%80%8b%e9%9d%9e%e7%a9%ba%e8%a1%a8%e9%81%94%e5%bc%8f%ef%bc%89","status":"publish","type":"post","link":"https:\/\/server.hk\/cnblog\/77918\/","title":{"rendered":"MySQL\u6307\u4ee4: COALESCE\uff08\u8fd4\u56de\u7b2c\u4e00\u500b\u975e\u7a7a\u8868\u9054\u5f0f\uff09"},"content":{"rendered":"<h1 id=\"mysql%e6%8c%87%e4%bb%a4-coalesce%ef%bc%88%e8%bf%94%e5%9b%9e%e7%ac%ac%e4%b8%80%e5%80%8b%e9%9d%9e%e7%a9%ba%e8%a1%a8%e9%81%94%e5%bc%8f%ef%bc%89-jflceMKrGh\">MySQL\u6307\u4ee4: COALESCE\uff08\u8fd4\u56de\u7b2c\u4e00\u500b\u975e\u7a7a\u8868\u9054\u5f0f\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\u662fCOALESCE\u51fd\u6578\u3002\u9019\u7bc7\u6587\u7ae0\u5c07\u6df1\u5165\u63a2\u8a0eCOALESCE\u7684\u7528\u6cd5\u3001\u8a9e\u6cd5\u53ca\u5176\u5728\u5be6\u969b\u61c9\u7528\u4e2d\u7684\u793a\u4f8b\u3002<\/p>\n<h2 id=\"coalesce%e5%87%bd%e6%95%b8%e6%a6%82%e8%bf%b0-jflceMKrGh\">COALESCE\u51fd\u6578\u6982\u8ff0<\/h2>\n<p>COALESCE\u51fd\u6578\u662f\u4e00\u500b\u7528\u65bc\u8fd4\u56de\u7b2c\u4e00\u500b\u975e\u7a7a\u8868\u9054\u5f0f\u7684SQL\u51fd\u6578\u3002\u7576\u4f60\u9700\u8981\u5f9e\u591a\u500b\u53ef\u80fd\u7684\u503c\u4e2d\u9078\u64c7\u4e00\u500b\u6709\u6548\u7684\u503c\u6642\uff0cCOALESCE\u975e\u5e38\u6709\u7528\u3002\u9019\u5728\u8655\u7406\u6578\u64da\u6642\uff0c\u7279\u5225\u662f\u7576\u6578\u64da\u4e2d\u53ef\u80fd\u5b58\u5728\u7a7a\u503c\u6642\uff0c\u80fd\u5920\u6709\u6548\u5730\u7c21\u5316\u67e5\u8a62\u3002<\/p>\n<h2 id=\"coalesce%e7%9a%84%e8%aa%9e%e6%b3%95-jflceMKrGh\">COALESCE\u7684\u8a9e\u6cd5<\/h2>\n<pre><code>COALESCE(value1, value2, ..., valueN)<\/code><\/pre>\n<p>\u5728\u9019\u88e1\uff0cvalue1, value2, &#8230;, valueN\u662f\u4f60\u5e0c\u671b\u6aa2\u67e5\u7684\u8868\u9054\u5f0f\u3002COALESCE\u5c07\u5f9e\u5de6\u5230\u53f3\u6aa2\u67e5\u9019\u4e9b\u503c\uff0c\u4e26\u8fd4\u56de\u7b2c\u4e00\u500b\u975e\u7a7a\u7684\u503c\u3002\u5982\u679c\u6240\u6709\u7684\u503c\u90fd\u662f\u7a7a\u7684\uff0c\u5247\u8fd4\u56deNULL\u3002<\/p>\n<h2 id=\"coalesce%e7%9a%84%e4%bd%bf%e7%94%a8%e7%a4%ba%e4%be%8b-jflceMKrGh\">COALESCE\u7684\u4f7f\u7528\u793a\u4f8b<\/h2>\n<p>\u4ee5\u4e0b\u662f\u4e00\u4e9b\u4f7f\u7528COALESCE\u7684\u5be6\u969b\u793a\u4f8b\uff0c\u5e6b\u52a9\u4f60\u66f4\u597d\u5730\u7406\u89e3\u5176\u61c9\u7528\u3002<\/p>\n<h3 id=\"%e7%a4%ba%e4%be%8b1-%e5%9f%ba%e6%9c%ac%e7%94%a8%e6%b3%95-jflceMKrGh\">\u793a\u4f8b1: \u57fa\u672c\u7528\u6cd5<\/h3>\n<p>\u5047\u8a2d\u6211\u5011\u6709\u4e00\u500b\u540d\u70baemployees\u7684\u8868\uff0c\u5305\u542b\u4ee5\u4e0b\u6b04\u4f4d\uff1aid, first_name, last_name, email\u3002\u67d0\u4e9b\u54e1\u5de5\u7684\u96fb\u5b50\u90f5\u4ef6\u5730\u5740\u53ef\u80fd\u662f\u7a7a\u7684\uff0c\u6211\u5011\u5e0c\u671b\u67e5\u8a62\u6bcf\u4f4d\u54e1\u5de5\u7684\u96fb\u5b50\u90f5\u4ef6\u5730\u5740\uff0c\u5982\u679c\u96fb\u5b50\u90f5\u4ef6\u5730\u5740\u70ba\u7a7a\uff0c\u5247\u8fd4\u56de\u5176\u5168\u540d\u3002<\/p>\n<pre><code>SELECT id, \n              COALESCE(email, CONCAT(first_name, ' ', last_name)) AS contact_info \n       FROM employees;<\/code><\/pre>\n<p>\u5728\u9019\u500b\u67e5\u8a62\u4e2d\uff0cCOALESCE\u51fd\u6578\u5c07\u6aa2\u67e5email\u6b04\u4f4d\uff0c\u5982\u679c\u8a72\u6b04\u4f4d\u70ba\u7a7a\uff0c\u5247\u8fd4\u56de\u7531first_name\u548clast_name\u7d44\u6210\u7684\u5168\u540d\u3002<\/p>\n<h3 id=\"%e7%a4%ba%e4%be%8b2-%e5%a4%9a%e5%80%8b%e5%80%bc%e7%9a%84%e8%99%95%e7%90%86-jflceMKrGh\">\u793a\u4f8b2: \u591a\u500b\u503c\u7684\u8655\u7406<\/h3>\n<p>\u5047\u8a2d\u6211\u5011\u6709\u4e00\u500b\u7522\u54c1\u8868products\uff0c\u5305\u542b\u6b04\u4f4d\uff1aid, name, price, discount_price\u3002\u6211\u5011\u5e0c\u671b\u67e5\u8a62\u6bcf\u500b\u7522\u54c1\u7684\u6700\u7d42\u50f9\u683c\uff0c\u5982\u679cdiscount_price\u5b58\u5728\uff0c\u5247\u4f7f\u7528\u5b83\uff0c\u5426\u5247\u4f7f\u7528price\u3002<\/p>\n<pre><code>SELECT id, \n              name, \n              COALESCE(discount_price, price) AS final_price \n       FROM products;<\/code><\/pre>\n<p>\u9019\u6a23\u7684\u67e5\u8a62\u5c07\u78ba\u4fdd\u6211\u5011\u59cb\u7d42\u7372\u5f97\u4e00\u500b\u6709\u6548\u7684\u50f9\u683c\uff0c\u7121\u8ad6\u662f\u6298\u6263\u50f9\u683c\u9084\u662f\u539f\u50f9\u3002<\/p>\n<h2 id=\"coalesce%e7%9a%84%e5%84%aa%e5%8b%a2-jflceMKrGh\">COALESCE\u7684\u512a\u52e2<\/h2>\n<ul>\n<li><strong>\u7c21\u5316\u67e5\u8a62\uff1a<\/strong>\u4f7f\u7528COALESCE\u53ef\u4ee5\u6e1b\u5c11\u9700\u8981\u7de8\u5beb\u7684\u689d\u4ef6\u8a9e\u53e5\uff0c\u5f9e\u800c\u4f7f\u67e5\u8a62\u66f4\u7c21\u6f54\u3002<\/li>\n<li><strong>\u63d0\u9ad8\u53ef\u8b80\u6027\uff1a<\/strong>COALESCE\u4f7f\u5f97\u67e5\u8a62\u7684\u610f\u5716\u66f4\u52a0\u660e\u78ba\uff0c\u4fbf\u65bc\u5176\u4ed6\u958b\u767c\u8005\u7406\u89e3\u3002<\/li>\n<li><strong>\u9748\u6d3b\u6027\uff1a<\/strong>\u53ef\u4ee5\u8655\u7406\u591a\u500b\u503c\uff0c\u4e26\u6839\u64da\u9700\u8981\u8fd4\u56de\u7b2c\u4e00\u500b\u6709\u6548\u503c\u3002<\/li>\n<\/ul>\n<h2 id=\"%e6%b3%a8%e6%84%8f%e4%ba%8b%e9%a0%85-jflceMKrGh\">\u6ce8\u610f\u4e8b\u9805<\/h2>\n<p>\u96d6\u7136COALESCE\u975e\u5e38\u6709\u7528\uff0c\u4f46\u5728\u4f7f\u7528\u6642\u4e5f\u9700\u8981\u6ce8\u610f\u4ee5\u4e0b\u5e7e\u9ede\uff1a<\/p>\n<ul>\n<li>COALESCE\u51fd\u6578\u7684\u8fd4\u56de\u985e\u578b\u53d6\u6c7a\u65bc\u5176\u53c3\u6578\u7684\u6578\u64da\u985e\u578b\uff0c\u53ef\u80fd\u6703\u5f71\u97ff\u67e5\u8a62\u7684\u7d50\u679c\u3002<\/li>\n<li>\u5728\u8655\u7406\u5927\u91cf\u6578\u64da\u6642\uff0c\u904e\u5ea6\u4f7f\u7528COALESCE\u53ef\u80fd\u6703\u5f71\u97ff\u67e5\u8a62\u6027\u80fd\uff0c\u56e0\u6b64\u61c9\u8b39\u614e\u4f7f\u7528\u3002<\/li>\n<\/ul>\n<h2 id=\"%e7%b8%bd%e7%b5%90-jflceMKrGh\">\u7e3d\u7d50<\/h2>\n<p>COALESCE\u51fd\u6578\u5728MySQL\u4e2d\u662f\u4e00\u500b\u5f37\u5927\u7684\u5de5\u5177\uff0c\u80fd\u5920\u5e6b\u52a9\u958b\u767c\u8005\u6709\u6548\u5730\u8655\u7406\u7a7a\u503c\u554f\u984c\u3002\u901a\u904e\u7c21\u5316\u67e5\u8a62\u548c\u63d0\u9ad8\u53ef\u8b80\u6027\uff0cCOALESCE\u4f7f\u5f97\u6578\u64da\u8655\u7406\u8b8a\u5f97\u66f4\u52a0\u9ad8\u6548\u3002\u5982\u679c\u4f60\u6b63\u5728\u5c0b\u627e\u7a69\u5b9a\u7684 <a href=\"https:\/\/server.hk\">\u9999\u6e2fVPS<\/a> \u89e3\u6c7a\u65b9\u6848\uff0cServer.HK\u63d0\u4f9b\u591a\u7a2e\u9078\u64c7\uff0c\u6eff\u8db3\u4e0d\u540c\u9700\u6c42\u7684\u7528\u6236\u3002\u7121\u8ad6\u662f <a href=\"https:\/\/server.hk\">\u96f2\u4f3a\u670d\u5668<\/a> \u9084\u662f <a href=\"https:\/\/server.hk\">\u9999\u6e2f\u4f3a\u670d\u5668<\/a>\uff0c\u6211\u5011\u90fd\u80fd\u70ba\u4f60\u63d0\u4f9b\u53ef\u9760\u7684\u652f\u6301\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"<p>\u4e86\u89e3MySQL\u6307\u4ee4COALESCE\uff0c\u8a72\u51fd\u6578\u8fd4\u56de\u7b2c\u4e00\u500b\u975e\u7a7a\u8868\u9054\u5f0f\uff0c\u5e6b\u52a9\u8655\u7406\u6578\u64da\u4e2d\u7684\u7a7a\u503c\u554f\u984c\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-77918","post","type-post","status-publish","format-standard","hentry","category-database"],"_links":{"self":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/77918","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=77918"}],"version-history":[{"count":1,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/77918\/revisions"}],"predecessor-version":[{"id":77919,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/77918\/revisions\/77919"}],"wp:attachment":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/media?parent=77918"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/categories?post=77918"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/tags?post=77918"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}