{"id":201090,"date":"2025-05-06T09:48:58","date_gmt":"2025-05-06T01:48:58","guid":{"rendered":"https:\/\/server.hk\/cnblog\/201090\/"},"modified":"2025-05-06T09:48:58","modified_gmt":"2025-05-06T01:48:58","slug":"explain-%e5%88%86%e6%9e%90%e7%bb%93%e6%9e%9c%e6%98%be%e7%a4%bausing-where%ef%bc%8c%e8%bf%99%e6%98%af%e5%90%a6%e6%84%8f%e5%91%b3%e7%9d%80%e6%9f%a5%e8%af%a2%e5%ad%98%e5%9c%a8%e5%9b%9e","status":"publish","type":"post","link":"https:\/\/server.hk\/cnblog\/201090\/","title":{"rendered":"Explain \u5206\u6790\u7ed3\u679c\u663e\u793a\u201cUsing where\u201d\uff0c\u8fd9\u662f\u5426\u610f\u5473\u7740\u67e5\u8be2\u5b58\u5728\u56de\u8868\u64cd\u4f5c\uff1f"},"content":{"rendered":"<p><b><\/b> <\/p>\n<h1>Explain \u5206\u6790\u7ed3\u679c\u663e\u793a\u201cUsing where\u201d\uff0c\u8fd9\u662f\u5426\u610f\u5473\u7740\u67e5\u8be2\u5b58\u5728\u56de\u8868\u64cd\u4f5c\uff1f<\/h1>\n<p>\u54c8\u55bd\uff01\u5927\u5bb6\u597d\uff0c\u5f88\u9ad8\u5174\u53c8\u89c1\u9762\u4e86\uff0c\u6211\u662f\u4e3b\u673a\u5b9d\u8d1d\u7684\u4e00\u540d\u4f5c\u8005\uff0c\u4eca\u5929\u7531\u6211\u7ed9\u5927\u5bb6\u5e26\u6765\u4e00\u7bc7\uff0c\u672c\u6587\u4e3b\u8981\u4f1a\u8bb2\u5230\u7b49\u7b49\u77e5\u8bc6\u70b9\uff0c\u5e0c\u671b\u5927\u5bb6\u4e00\u8d77\u5b66\u4e60\u8fdb\u6b65\uff0c\u4e5f\u6b22\u8fce\u5927\u5bb6\u5173\u6ce8\u3001\u70b9\u8d5e\u3001\u6536\u85cf\u3001\u8f6c\u53d1! \u4e0b\u9762\u5c31\u4e00\u8d77\u6765\u770b\u770b\u5427\uff01<\/p>\n<p><img decoding=\"async\" src=\"https:\/\/www.17golang.com\/uploads\/20241130\/1732974520674b17b8d9a76.jpg\" class=\"aligncenter\"><\/p>\n<p><strong>\u5224\u65ad\u56de\u8868\u64cd\u4f5c\uff1aexplain \u5206\u6790<\/strong><\/p>\n<p>\u6839\u636e\u4f60\u7684\u95ee\u9898\uff0c\u4f60\u53ef\u4ee5\u901a\u8fc7 explain \u7684 extra \u5b57\u6bb5\u6765\u5224\u65ad\u67e5\u8be2\u662f\u5426\u5b58\u5728\u56de\u8868\u64cd\u4f5c\u3002<\/p>\n<p><strong>extra \u5b57\u6bb5\u89e3\u91ca\uff1a<\/strong><\/p>\n<ul>\n<li><strong>using index\uff1a<\/strong>\u4f7f\u7528\u7d22\u5f15\u8986\u76d6\uff0c\u67e5\u8be2\u5b57\u6bb5\u5168\u90e8\u5728\u7d22\u5f15\u4e2d\uff0c\u4e0d\u9700\u8981\u56de\u8868\u3002<\/li>\n<li><strong>using index condition\uff1a<\/strong>\u4f7f\u7528\u7d22\u5f15\u67e5\u627e\uff0c\u4f46\u9700\u8981\u6839\u636e\u8fc7\u6ee4\u6761\u4ef6\u5224\u65ad\uff0c\u4e5f\u4e0d\u9700\u8981\u56de\u8868\u3002<\/li>\n<li><strong>using index with where:<\/strong> \u4f7f\u7528\u7d22\u5f15\uff0c\u4f46\u9700\u8981\u6839\u636e where \u6761\u4ef6\u8fc7\u6ee4\uff0c\u9700\u8981\u56de\u8868\u3002<\/li>\n<\/ul>\n<p><strong>\u6848\u4f8b\u5206\u6790\uff1a<\/strong><\/p>\n<p>\u4f60\u63d0\u4f9b\u7684 explain \u8f93\u51fa\u4e2d\uff0cextra \u4e3a\uff1a<\/p>\n<pre>Using where; Using index; Using temporary; Using filesort<\/pre>\n<p>\u7531\u4e8e extra \u4e2d\u5305\u542b &#8220;using where&#8221;\uff0c\u8fd9\u610f\u5473\u7740\u67e5\u8be2\u9700\u8981\u56de\u8868\u64cd\u4f5c\u3002<\/p>\n<p><strong>\u7ed3\u8bba\uff1a<\/strong><\/p>\n<p>\u56e0\u6b64\uff0c\u6839\u636e explain \u5206\u6790\u7684\u7ed3\u679c\uff0c\u4f60\u7684\u67e5\u8be2\u8fd8\u5b58\u5728\u56de\u8868\u64cd\u4f5c\u3002<\/p>\n<p>\u672c\u7bc7\u5173\u4e8e\u300aExplain \u5206\u6790\u7ed3\u679c\u663e\u793a\u201cUsing where\u201d\uff0c\u8fd9\u662f\u5426\u610f\u5473\u7740\u67e5\u8be2\u5b58\u5728\u56de\u8868\u64cd\u4f5c\uff1f\u300b\u7684\u4ecb\u7ecd\u5c31\u5230\u6b64\u7ed3\u675f\u5566\uff0c\u4f46\u662f\u5b66\u65e0\u6b62\u5883\uff0c\u60f3\u8981\u4e86\u89e3\u5b66\u4e60\u66f4\u591a\u5173\u4e8e\u6570\u636e\u5e93\u7684\u76f8\u5173\u77e5\u8bc6\uff0c\u8bf7\u5173\u6ce8\u4e3b\u673a\u5b9d\u8d1d\u516c\u4f17\u53f7\uff01<\/p>\n<dl>\n<dt>\n <\/dt>\n<\/dl>\n","protected":false},"excerpt":{"rendered":"<p>Explain \u5206\u6790\u7ed3\u679c\u663e\u793a\u201cU&#46;&#46;&#46;<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[101],"tags":[],"class_list":["post-201090","post","type-post","status-publish","format-standard","hentry","category-database"],"_links":{"self":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/201090","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"}],"author":[{"embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/comments?post=201090"}],"version-history":[{"count":0,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/201090\/revisions"}],"wp:attachment":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/media?parent=201090"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/categories?post=201090"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/tags?post=201090"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}