{"id":289,"date":"2009-06-23T02:16:02","date_gmt":"2009-06-22T18:16:02","guid":{"rendered":"http:\/\/wp.chunhsin.idv.tw\/?p=289"},"modified":"2009-06-23T02:16:13","modified_gmt":"2009-06-22T18:16:13","slug":"%e4%bb%8a%e5%a4%a9%e4%bd%bf%e7%94%a8mysql%e7%9a%84if%e5%87%bd%e6%95%b8","status":"publish","type":"post","link":"https:\/\/wp.chunhsin.idv.tw\/?p=289","title":{"rendered":"\u4eca\u5929\u4f7f\u7528mysql\u7684if()\u51fd\u6578"},"content":{"rendered":"<p>\u4eca\u5929\u4f7f\u7528mysql\u7684<span style=\"color: #ff6600;\">if<\/span>()\u51fd\u6578\uff0c\u642d\u914d<span style=\"color: #ff6600;\">count<\/span>()\u51fd\u6578\u4f86\u8a08\u7b97\u67d0\u500b\u6b04\u4f4d\u7684\u6578\u91cf\uff0c\u4f8b\u5982\u6b04\u4f4d\u540d\u662f<span style=\"color: #993300;\">reg_date<\/span>\uff0c\u51fd\u6578\u7528\u6cd5\u662f<span style=\"color: #0000ff;\"><span style=\"color: #ff6600;\">if<\/span>(<span style=\"color: #993300;\">reg_date<\/span> is <strong>null<\/strong>, &#8221;,<span style=\"color: #ff6600;\">count<\/span>(<span style=\"color: #993300;\">reg_date<\/span>)) as <span style=\"color: #993300;\">nums<\/span><\/span>\u3002\u610f\u601d\u5c31\u662f\u7576<span style=\"color: #993300;\">reg_date<\/span>\u662f<span style=\"color: #0000ff;\">null<\/span>\u7684\u6642\u5019\u5c31\u4ec0\u9ebc\u90fd\u4e0d\u505a\uff0c\u5982\u679c\u4e0d\u662f<span style=\"color: #0000ff;\">null<\/span>\u5c31\u7d2f\u8a08\u6578\u91cf\u3002<!--more--><\/p>\n<p>\u56e0\u70ba\u662f\u5728select\u6558\u8ff0\u4e0b\u6240\u4f7f\u7528\uff0c\u6240\u4ee5<span style=\"color: #ff6600;\">if<\/span>\u50b3\u56de\u7684\u7d50\u679c\u5c31\u662f\u4e00\u500b\u6b04\u4f4d\uff0c\u6240\u4ee5\u52a0\u4e0a<span style=\"color: #0000ff;\">as<\/span>\u91cd\u65b0\u547d\u540d\u70ba<span style=\"color: #993300;\">nums<\/span>\u3002<\/p>\n<p><span style=\"color: #ff6600;\">count<\/span>\u662fmysql\u7684\u96c6\u5408\u51fd\u6578\uff0c\u4e5f\u5c31\u662f\u5728\u6709<span style=\"color: #0000ff;\">group by<\/span>\u7684\u689d\u4ef6\u4e0b\u4f7f\u7528\u7684\u51fd\u6578\uff0c\u5176\u5be6\u5230\u76ee\u524d\u70ba\u6b62\u5c0d\u9019\u985e\u96c6\u5408\u51fd\u6578\u7684\u4f7f\u7528\u53ca\u6982\u5ff5\u9084\u4e0d\u662f\u592a\u6e05\u695a\uff0c\u4e5f\u8a31\u662f\u56e0\u70ba\u4e00\u958b\u59cb\u78b0\u7684\u8cc7\u6599\u5eab\u8edf\u9ad4\u662f<span style=\"color: #00ccff;\">Access<\/span>\uff0c\u90a3\u6642\u5019\u662f\u4f7f\u7528\u62d6\u62c9\u7684\u65b9\u5f0f\u5728\u67e5\u8a62\uff0c\u4e0d\u5e38\u76f4\u63a5\u78b0\u89f8sql\u8a9e\u6cd5\uff0c\u518d\u52a0\u4e0a\u5c0d\u65bcphp\u7684count\u7684\u5370\u8c61\uff0c\u6240\u4ee5\u5c0d\u65bc\u5728mysql\u4f7f\u7528\u96c6\u5408\u51fd\u6578\u6642\u7e3d\u662f\u64d4\u5fc3\u7d50\u679c\u7570\u5e38\u7684\u72c0\u6cc1\u6703\u767c\u751f\u3002<\/p>\n<p>\u4e0d\u904e\u4eca\u5929\u4f7f\u7528\u7684\u7d50\u679c\u662f\u5c0f\u5c0f\u589e\u52a0\u4e86\u81ea\u5df1\u5728\u4f7f\u7528\u9019\u985e\u96c6\u5408\u51fd\u6578\u7684\u4fe1\u5fc3\u4e86\u3002\u4eca\u5929\u89c0\u5bdf\u5b83\u57f7\u884c\u7684\u7d50\u679c\uff0c\u96c6\u5408\u51fd\u6578\u61c9\u8a72\u662f\u5728select\u7d50\u679c\u6642\u9010\u6b04\u3001\u9010\u5217\u57f7\u884c\uff0c<span style=\"color: #808000;\">\u6700\u5f8c\u624d\u5448\u73fe\u51fa\u904b\u7b97\u7684\u7d50\u679c\u3002<\/span>\u5982\u679c\u6309\u9019\u500b\u539f\u7406\u4f86\u770b\u5f85\u96c6\u5408\u51fd\u6578\u904b\u4f5c\uff0c\u9019\u6a23\u61c9\u8a72\u5c31\u6703\u6bd4\u8f03\u6e05\u695a\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"<p>\u4eca\u5929\u4f7f\u7528mysql\u7684if()\u51fd\u6578\uff0c\u642d\u914dcount()\u51fd\u6578\u4f86\u8a08\u7b97\u67d0\u500b\u6b04\u4f4d\u7684\u6578\u91cf\uff0c\u4f8b\u5982\u6b04\u4f4d\u540d\u662freg_date\uff0c\u51fd &hellip; <a href=\"https:\/\/wp.chunhsin.idv.tw\/?p=289\" class=\"more-link\">\u95b1\u8b80\u5168\u6587<span class=\"screen-reader-text\">\u3008\u4eca\u5929\u4f7f\u7528mysql\u7684if()\u51fd\u6578\u3009<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[8],"tags":[],"class_list":["post-289","post","type-post","status-publish","format-standard","hentry","category-mysql"],"_links":{"self":[{"href":"https:\/\/wp.chunhsin.idv.tw\/index.php?rest_route=\/wp\/v2\/posts\/289","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/wp.chunhsin.idv.tw\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/wp.chunhsin.idv.tw\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/wp.chunhsin.idv.tw\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/wp.chunhsin.idv.tw\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=289"}],"version-history":[{"count":6,"href":"https:\/\/wp.chunhsin.idv.tw\/index.php?rest_route=\/wp\/v2\/posts\/289\/revisions"}],"predecessor-version":[{"id":295,"href":"https:\/\/wp.chunhsin.idv.tw\/index.php?rest_route=\/wp\/v2\/posts\/289\/revisions\/295"}],"wp:attachment":[{"href":"https:\/\/wp.chunhsin.idv.tw\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=289"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/wp.chunhsin.idv.tw\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=289"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/wp.chunhsin.idv.tw\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=289"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}