{"id":81416,"date":"2024-10-16T15:37:20","date_gmt":"2024-10-16T07:37:20","guid":{"rendered":"https:\/\/server.hk\/cnblog\/81416\/"},"modified":"2024-10-16T15:37:20","modified_gmt":"2024-10-16T07:37:20","slug":"null%e8%88%87mysql%e7%a9%ba%e5%ad%97%e7%ac%a6%e4%b8%b2%e7%9a%84%e5%8d%80%e5%88%a5","status":"publish","type":"post","link":"https:\/\/server.hk\/cnblog\/81416\/","title":{"rendered":"NULL\u8207MySQL\u7a7a\u5b57\u7b26\u4e32\u7684\u5340\u5225"},"content":{"rendered":"<h1 id=\"null%e8%88%87mysql%e7%a9%ba%e5%ad%97%e7%ac%a6%e4%b8%b2%e7%9a%84%e5%8d%80%e5%88%a5-jafOkuJrOX\">NULL\u8207MySQL\u7a7a\u5b57\u7b26\u4e32\u7684\u5340\u5225<\/h1>\n<p>\u5728\u6578\u64da\u5eab\u7ba1\u7406\u7cfb\u7d71\u4e2d\uff0c\u7279\u5225\u662fMySQL\u4e2d\uff0cNULL\u548c\u7a7a\u5b57\u7b26\u4e32\uff08&#8221;&#8221;\uff09\u662f\u5169\u500b\u5e38\u898b\u4f46\u5bb9\u6613\u6df7\u6dc6\u7684\u6982\u5ff5\u3002\u7406\u89e3\u9019\u5169\u8005\u4e4b\u9593\u7684\u5340\u5225\u5c0d\u65bc\u6578\u64da\u5eab\u8a2d\u8a08\u548c\u67e5\u8a62\u512a\u5316\u81f3\u95dc\u91cd\u8981\u3002\u672c\u6587\u5c07\u6df1\u5165\u63a2\u8a0eNULL\u548c\u7a7a\u5b57\u7b26\u4e32\u7684\u5b9a\u7fa9\u3001\u4f7f\u7528\u60c5\u5883\u53ca\u5176\u5728MySQL\u4e2d\u7684\u884c\u70ba\u3002<\/p>\n<h2 id=\"null%e7%9a%84%e5%ae%9a%e7%be%a9-jafOkuJrOX\">NULL\u7684\u5b9a\u7fa9<\/h2>\n<p>NULL\u662f\u4e00\u500b\u7279\u6b8a\u7684\u6a19\u8a18\uff0c\u7528\u4f86\u8868\u793a\u201c\u7121\u503c\u201d\u6216\u201c\u672a\u77e5\u201d\u3002\u5728\u6578\u64da\u5eab\u4e2d\uff0cNULL\u4e26\u4e0d\u7b49\u540c\u65bc\u96f6\u6216\u7a7a\u5b57\u7b26\u4e32\uff0c\u5b83\u8868\u793a\u4e00\u500b\u7f3a\u5931\u7684\u6578\u64da\u3002\u7576\u4e00\u500b\u5b57\u6bb5\u88ab\u8a2d\u7f6e\u70baNULL\u6642\uff0c\u9019\u610f\u5473\u8457\u8a72\u5b57\u6bb5\u6c92\u6709\u4efb\u4f55\u6709\u6548\u7684\u6578\u64da\u3002<\/p>\n<h2 id=\"%e7%a9%ba%e5%ad%97%e7%ac%a6%e4%b8%b2%e7%9a%84%e5%ae%9a%e7%be%a9-jafOkuJrOX\">\u7a7a\u5b57\u7b26\u4e32\u7684\u5b9a\u7fa9<\/h2>\n<p>\u7a7a\u5b57\u7b26\u4e32\uff08&#8221;&#8221;\uff09\u662f\u4e00\u500b\u6709\u6548\u7684\u5b57\u7b26\u4e32\u985e\u578b\uff0c\u8868\u793a\u4e00\u500b\u9577\u5ea6\u70ba\u96f6\u7684\u5b57\u7b26\u4e32\u3002\u9019\u610f\u5473\u8457\u8a72\u5b57\u6bb5\u5b58\u5728\uff0c\u4f46\u5176\u5167\u5bb9\u70ba\u7a7a\u3002\u7a7a\u5b57\u7b26\u4e32\u548cNULL\u7684\u4e3b\u8981\u5340\u5225\u5728\u65bc\uff0c\u7a7a\u5b57\u7b26\u4e32\u662f\u6709\u610f\u7fa9\u7684\u5b58\u5728\uff0c\u800cNULL\u5247\u8868\u793a\u7f3a\u5931\u6216\u672a\u77e5\u7684\u6578\u64da\u3002<\/p>\n<h2 id=\"null%e8%88%87%e7%a9%ba%e5%ad%97%e7%ac%a6%e4%b8%b2%e7%9a%84%e8%a1%8c%e7%82%ba%e6%af%94%e8%bc%83-jafOkuJrOX\">NULL\u8207\u7a7a\u5b57\u7b26\u4e32\u7684\u884c\u70ba\u6bd4\u8f03<\/h2>\n<p>\u5728MySQL\u4e2d\uff0cNULL\u548c\u7a7a\u5b57\u7b26\u4e32\u5728\u67e5\u8a62\u548c\u64cd\u4f5c\u6642\u7684\u884c\u70ba\u6709\u6240\u4e0d\u540c\u3002\u4ee5\u4e0b\u662f\u4e00\u4e9b\u95dc\u9375\u7684\u6bd4\u8f03\uff1a<\/p>\n<ul>\n<li><strong>\u6bd4\u8f03\u64cd\u4f5c\uff1a<\/strong>\u5728MySQL\u4e2d\uff0c\u4efb\u4f55\u8207NULL\u7684\u6bd4\u8f03\u90fd\u6703\u8fd4\u56deNULL\u3002\u4f8b\u5982\uff0c\u4ee5\u4e0b\u67e5\u8a62\u5c07\u4e0d\u6703\u8fd4\u56de\u4efb\u4f55\u7d50\u679c\uff1a<\/li>\n<pre><code>SELECT * FROM users WHERE username = NULL;<\/code><\/pre>\n<li>\u76f8\u53cd\uff0c\u7a7a\u5b57\u7b26\u4e32\u53ef\u4ee5\u9032\u884c\u6bd4\u8f03\uff0c\u4e26\u4e14\u53ef\u4ee5\u7528\u65bc\u67e5\u8a62\u3002\u4f8b\u5982\uff1a<\/li>\n<pre><code>SELECT * FROM users WHERE username = '';<\/code><\/pre>\n<li><strong>\u805a\u5408\u51fd\u6578\uff1a<\/strong>\u5728\u4f7f\u7528\u805a\u5408\u51fd\u6578\u6642\uff0cNULL\u503c\u6703\u88ab\u5ffd\u7565\uff0c\u800c\u7a7a\u5b57\u7b26\u4e32\u5247\u6703\u88ab\u8a08\u7b97\u3002\u4f8b\u5982\uff1a<\/li>\n<pre><code>SELECT COUNT(*) FROM users WHERE username IS NULL; -- \u8a08\u7b97NULL\u7684\u6578\u91cf\nSELECT COUNT(*) FROM users WHERE username = ''; -- \u8a08\u7b97\u7a7a\u5b57\u7b26\u4e32\u7684\u6578\u91cf<\/code><\/pre>\n<\/ul>\n<h2 id=\"%e4%bd%bf%e7%94%a8%e6%83%85%e5%a2%83-jafOkuJrOX\">\u4f7f\u7528\u60c5\u5883<\/h2>\n<p>\u5728\u8a2d\u8a08\u6578\u64da\u5eab\u6642\uff0c\u9078\u64c7\u4f7f\u7528NULL\u9084\u662f\u7a7a\u5b57\u7b26\u4e32\u53d6\u6c7a\u65bc\u5177\u9ad4\u7684\u696d\u52d9\u9700\u6c42\u3002\u4ee5\u4e0b\u662f\u4e00\u4e9b\u5efa\u8b70\uff1a<\/p>\n<ul>\n<li>\u5982\u679c\u67d0\u500b\u5b57\u6bb5\u7684\u503c\u662f\u53ef\u9078\u7684\uff0c\u4e14\u53ef\u80fd\u4e0d\u5b58\u5728\uff0c\u5247\u61c9\u4f7f\u7528NULL\u3002\u4f8b\u5982\uff0c\u4f7f\u7528\u8005\u7684\u4e2d\u9593\u540d\u53ef\u80fd\u4e0d\u9069\u7528\u65bc\u6240\u6709\u4f7f\u7528\u8005\u3002<\/li>\n<li>\u5982\u679c\u67d0\u500b\u5b57\u6bb5\u5fc5\u9808\u5b58\u5728\uff0c\u4f46\u5176\u5167\u5bb9\u53ef\u80fd\u70ba\u7a7a\uff0c\u5247\u61c9\u4f7f\u7528\u7a7a\u5b57\u7b26\u4e32\u3002\u4f8b\u5982\uff0c\u4f7f\u7528\u8005\u7684\u5099\u8a3b\u5b57\u6bb5\u53ef\u4ee5\u662f\u7a7a\u7684\uff0c\u4f46\u4ecd\u7136\u9700\u8981\u5728\u6578\u64da\u5eab\u4e2d\u5b58\u5728\u3002<\/li>\n<\/ul>\n<h2 id=\"%e5%af%a6%e9%9a%9b%e7%af%84%e4%be%8b-jafOkuJrOX\">\u5be6\u969b\u7bc4\u4f8b<\/h2>\n<p>\u8003\u616e\u4e00\u500b\u7528\u6236\u8cc7\u6599\u8868\uff0c\u5305\u542b\u4ee5\u4e0b\u5b57\u6bb5\uff1a<\/p>\n<pre><code>CREATE TABLE users (\n    id INT AUTO_INCREMENT PRIMARY KEY,\n    username VARCHAR(50) NOT NULL,\n    middle_name VARCHAR(50) DEFAULT NULL,\n    notes TEXT DEFAULT ''\n);<\/code><\/pre>\n<p>\u5728\u9019\u500b\u4f8b\u5b50\u4e2d\uff0cmiddle_name\u5b57\u6bb5\u53ef\u4ee5\u70baNULL\uff0c\u8868\u793a\u7528\u6236\u6c92\u6709\u4e2d\u9593\u540d\uff0c\u800cnotes\u5b57\u6bb5\u5247\u53ef\u4ee5\u662f\u7a7a\u5b57\u7b26\u4e32\uff0c\u8868\u793a\u7528\u6236\u6c92\u6709\u4efb\u4f55\u5099\u8a3b\u3002<\/p>\n<h2 id=\"%e7%b5%90%e8%ab%96-jafOkuJrOX\">\u7d50\u8ad6<\/h2>\n<p>NULL\u548c\u7a7a\u5b57\u7b26\u4e32\u5728MySQL\u4e2d\u6709\u8457\u660e\u986f\u7684\u5340\u5225\uff0c\u7406\u89e3\u9019\u4e9b\u5dee\u7570\u5c0d\u65bc\u6578\u64da\u5eab\u7684\u8a2d\u8a08\u548c\u67e5\u8a62\u81f3\u95dc\u91cd\u8981\u3002\u9078\u64c7\u6b63\u78ba\u7684\u6578\u64da\u985e\u578b\u53ef\u4ee5\u5e6b\u52a9\u63d0\u9ad8\u6578\u64da\u7684\u6e96\u78ba\u6027\u548c\u67e5\u8a62\u7684\u6548\u7387\u3002\u5728\u8a2d\u8a08\u6578\u64da\u5eab\u6642\uff0c\u958b\u767c\u8005\u61c9\u6839\u64da\u5177\u9ad4\u9700\u6c42\u4f86\u6c7a\u5b9a\u4f55\u6642\u4f7f\u7528NULL\uff0c\u4f55\u6642\u4f7f\u7528\u7a7a\u5b57\u7b26\u4e32\u3002<\/p>\n<p>\u5982\u9700\u4e86\u89e3\u66f4\u591a\u95dc\u65bc\u6578\u64da\u5eab\u7ba1\u7406\u548c\u512a\u5316\u7684\u8cc7\u8a0a\uff0c\u8acb\u8a2a\u554f\u6211\u5011\u7684\u7db2\u7ad9 <a href=\"https:\/\/server.hk\">Server.HK<\/a>\uff0c\u6211\u5011\u63d0\u4f9b\u5404\u7a2e <a href=\"https:\/\/server.hk\">VPS<\/a> \u89e3\u6c7a\u65b9\u6848\uff0c\u5e6b\u52a9\u60a8\u66f4\u597d\u5730\u7ba1\u7406\u60a8\u7684\u6578\u64da\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"<p>\u4e86\u89e3NULL\u8207MySQL\u7a7a\u5b57\u7b26\u4e32\u7684\u5340\u5225\uff0c\u63a2\u8a0e\u5176\u5728\u6578\u64da\u5eab\u4e2d\u7684\u610f\u7fa9\u53ca\u4f7f\u7528\u60c5\u5883\uff0c\u63d0\u5347\u6578\u64da\u8655\u7406\u7684\u6e96\u78ba\u6027\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-81416","post","type-post","status-publish","format-standard","hentry","category-database"],"_links":{"self":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/81416","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=81416"}],"version-history":[{"count":1,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/81416\/revisions"}],"predecessor-version":[{"id":81417,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/81416\/revisions\/81417"}],"wp:attachment":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/media?parent=81416"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/categories?post=81416"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/tags?post=81416"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}