{"id":1351,"date":"2024-02-20T18:43:27","date_gmt":"2024-02-20T10:43:27","guid":{"rendered":"https:\/\/blog.humh.cn\/?p=1351"},"modified":"2024-02-20T18:43:27","modified_gmt":"2024-02-20T10:43:27","slug":"mysql-%e8%8e%b7%e5%8f%96%e6%8c%87%e5%ae%9a%e5%ad%97%e6%ae%b5%e6%9c%80%e5%90%8e%e4%b8%80%e4%b8%aa%e5%ad%97%e7%ac%a6","status":"publish","type":"post","link":"https:\/\/blog.humh.cn\/?p=1351","title":{"rendered":"mysql \u83b7\u53d6\u6307\u5b9a\u5b57\u6bb5\u6700\u540e\u4e00\u4e2a\u5b57\u7b26"},"content":{"rendered":"\n<p>\u5047\u8bbe\u73b0\u5728\u6709\u4e00\u4e2a\u8868 tab\uff0c\u5982\u4e0b<\/p>\n\n\n\n<pre class=\"EnlighterJSRAW\" data-enlighter-language=\"sql\" data-enlighter-theme=\"\" data-enlighter-highlight=\"\" data-enlighter-linenumbers=\"\" data-enlighter-lineoffset=\"\" data-enlighter-title=\"\" data-enlighter-group=\"\">with tab as (\n    select 'abcde' as str\n)<\/pre>\n\n\n\n<p>\u82e5\u60f3\u67e5\u8be2`str`\u5b57\u6bb5\u7684\u7b2c n \u4f4d\u5b57\u7b26\uff0c\u53ef\u4ee5\u901a\u8fc7 substring \u51fd\u6570\u5b8c\u6210\uff0c\u51fd\u6570\u652f\u6301 2~3 \u4e2a\u53c2\u6570\u3002<\/p>\n\n\n\n<ul><li>\u53c2\u65701\uff1a\u5b57\u6bb5\u540d\uff1b<\/li><li>\u53c2\u65702\uff1a\u8d77\u59cb\u4f4d\u7f6en\uff0c\u4ece\u5de6\u5f80\u53f3\u622a\u53d6\u5219\u4ece 1 \u5f00\u59cb\uff08\u6ce8\u610f\u4e0d\u662f\u4ece 0\uff01\u5927\u90e8\u5206\u8bed\u8a00\u662f\u4ece 0 \u5f00\u59cb\uff0c\u5982 java String\u7c7b\uff09\uff1b\u4ece\u53f3\u5f80\u5de6\u5219\u4ece -1 \u5f00\u59cb\uff1b<\/li><li>\u53c2\u65703\uff1a\u9700\u8981\u622a\u53d6\u7684\u5b50\u4e32\u957f\u5ea6 m\uff0c\u82e5 m \u8d85\u51fa\u53ef\u622a\u53d6\u957f\u5ea6\u9650\u5236\uff0c\u5219\u81f3\u591a\u5230\u5c3e\uff1b\u82e5\u4e0d\u586b\uff0c\u5219\u5230\u5b57\u4e32\u7ed3\u5c3e\uff1b<\/li><\/ul>\n\n\n\n<p>1\u3001\u60f3\u8981\u622a\u53d6\u51fa`str`\u5b57\u6bb5\u7684\u7b2c 1 \u4f4d<\/p>\n\n\n\n<pre class=\"EnlighterJSRAW\" data-enlighter-language=\"sql\" data-enlighter-theme=\"\" data-enlighter-highlight=\"\" data-enlighter-linenumbers=\"\" data-enlighter-lineoffset=\"\" data-enlighter-title=\"\" data-enlighter-group=\"\">-- \u8f93\u51fa\uff1aa\nselect substring(str, 1, 1) from tab;<\/pre>\n\n\n\n<p>2\u3001\u60f3\u8981\u622a\u53d6\u51fa`str`\u5b57\u6bb5\u7684\u7b2c 4~5 \u4f4d<\/p>\n\n\n\n<pre class=\"EnlighterJSRAW\" data-enlighter-language=\"sql\" data-enlighter-theme=\"\" data-enlighter-highlight=\"\" data-enlighter-linenumbers=\"\" data-enlighter-lineoffset=\"\" data-enlighter-title=\"\" data-enlighter-group=\"\">-- \u8f93\u51fa\uff1ade\nselect substring(str, 4, 2) from tab;\nselect substring(str, 4) from tab; -- \u8fd9\u91cc`str`\u5b57\u6bb5\u957f\u5ea6\u56fa\u5b9a\u4e3a 5 \u4f4d\uff0c\u5219\u957f\u5ea6\u6307\u5b9a\u53ef\u7701\u7565\nselect substring(str, -2, 2) from tab; -- \u8fd9\u91cc`str`\u5b57\u6bb5\u957f\u5ea6\u56fa\u5b9a\u4e3a 5 \u4f4d\uff0c\u5219\u7b2c 4 \u4f4d\u4e5f\u662f\u5012\u6570\u7b2c 2 \u4f4d\nselect substring(str, -2) from tab;<\/pre>\n\n\n\n<p>\u7efc\u4e0a\uff0c\u60f3\u8981\u622a\u53d6\u51fa`str`\u5b57\u6bb5\u7684\u6700\u540e\u4e00\u4f4d\u5b57\u7b26\uff0c\u5219\u53ef<\/p>\n\n\n\n<pre class=\"EnlighterJSRAW\" data-enlighter-language=\"sql\" data-enlighter-theme=\"\" data-enlighter-highlight=\"\" data-enlighter-linenumbers=\"\" data-enlighter-lineoffset=\"\" data-enlighter-title=\"\" data-enlighter-group=\"\">select substring(str, 5, 1) from tab;\nselect substring(str, 5) from tab;\nselect substring(str, length(str)) from tab; -- \u82e5\u5b57\u6bb5\u957f\u5ea6\u4e0d\u56fa\u5b9a\u6216\u672a\u77e5\uff0c\u5219\u53ef\u914d\u5408 length \u51fd\u6570\u52a8\u6001\u83b7\u53d6\u6700\u540e\u4e00\u4f4d\u5bf9\u5e94\u4f4d\u7f6e<\/pre>\n","protected":false},"excerpt":{"rendered":"<p>\u5047\u8bbe\u73b0\u5728\u6709\u4e00\u4e2a\u8868 tab\uff0c\u5982\u4e0b \u82e5\u60f3\u67e5\u8be2`str`\u5b57\u6bb5\u7684\u7b2c n \u4f4d\u5b57\u7b26\uff0c\u53ef\u4ee5\u901a\u8fc7 substring \u51fd\u6570\u5b8c\u6210 [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[52],"tags":[36],"_links":{"self":[{"href":"https:\/\/blog.humh.cn\/index.php?rest_route=\/wp\/v2\/posts\/1351"}],"collection":[{"href":"https:\/\/blog.humh.cn\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blog.humh.cn\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blog.humh.cn\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/blog.humh.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=1351"}],"version-history":[{"count":1,"href":"https:\/\/blog.humh.cn\/index.php?rest_route=\/wp\/v2\/posts\/1351\/revisions"}],"predecessor-version":[{"id":1352,"href":"https:\/\/blog.humh.cn\/index.php?rest_route=\/wp\/v2\/posts\/1351\/revisions\/1352"}],"wp:attachment":[{"href":"https:\/\/blog.humh.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=1351"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blog.humh.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=1351"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blog.humh.cn\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=1351"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}