{"id":3700,"date":"2025-05-10T18:05:14","date_gmt":"2025-05-10T10:05:14","guid":{"rendered":"https:\/\/www.laixuexila.com\/?p=3700"},"modified":"2025-05-10T18:05:14","modified_gmt":"2025-05-10T10:05:14","slug":"null-%e5%92%8c-%e7%a9%ba%e5%ad%97%e7%ac%a6%e4%b8%b2-%e4%b9%8b%e9%97%b4%e7%9a%84%e5%8c%ba%e5%88%ab","status":"publish","type":"post","link":"https:\/\/www.laixuexila.com\/index.php\/2025\/05\/10\/null-%e5%92%8c-%e7%a9%ba%e5%ad%97%e7%ac%a6%e4%b8%b2-%e4%b9%8b%e9%97%b4%e7%9a%84%e5%8c%ba%e5%88%ab\/","title":{"rendered":"NULL\u00a0\u548c\u00a0\u7a7a\u5b57\u7b26\u4e32 (&#8220;&#8221;)\u00a0\u4e4b\u95f4\u7684\u533a\u522b"},"content":{"rendered":"\n<p><strong>MySQL \u4e0d\u5efa\u8bae\u4f7f\u7528 NULL \u4f5c\u4e3a\u5217\u7684\u9ed8\u8ba4\u503c<\/strong> \u4e0e <strong>NULL<\/strong> \u548c <strong>\u7a7a\u5b57\u7b26\u4e32 (&#8220;&#8221;)<\/strong> \u4e4b\u95f4\u7684\u533a\u522b\u662f\u5bc6\u5207\u76f8\u5173\u7684\u3002\u5728\u6570\u636e\u5e93\u8bbe\u8ba1\u4e2d\uff0c<strong>NULL<\/strong> \u548c <strong>\u7a7a\u5b57\u7b26\u4e32<\/strong> \u770b\u4f3c\u76f8\u4f3c\uff0c\u4f46\u5b9e\u9645\u4e0a\u5b83\u4eec\u6709\u672c\u8d28\u533a\u522b\uff0c\u7279\u522b\u662f\u5728\u5904\u7406\u6570\u636e\u65f6\u7684\u542b\u4e49\u548c\u884c\u4e3a\u3002<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">\u4e00\u3001<strong>NULL \u548c \u7a7a\u5b57\u7b26\u4e32 (&#8220;&#8221;) \u7684\u533a\u522b<\/strong><\/h3>\n\n\n\n<h4 class=\"wp-block-heading\">1\u3001<strong>NULL<\/strong>:<\/h4>\n\n\n\n<ol class=\"wp-block-list\"><\/ol>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>\u542b\u4e49<\/strong>\uff1a\u8868\u793a\u201c\u65e0\u503c\u201d\u6216\u201c\u7f3a\u5931\u7684\u503c\u201d\u3002NULL \u503c\u901a\u5e38\u7528\u4e8e\u8868\u793a\u6570\u636e\u5728\u67d0\u4e00\u5217\u4e2d\u7f3a\u5931\u6216\u672a\u77e5\uff0c\u5e76\u4e0d\u662f\u4e00\u4e2a\u5177\u4f53\u7684\u503c\u3002\u5b83\u610f\u5473\u7740\u8be5\u5b57\u6bb5\u6ca1\u6709\u88ab\u8d4b\u503c\uff0c\u4e5f\u6ca1\u6709\u6570\u636e\u3002<\/li>\n\n\n\n<li><strong>\u884c\u4e3a<\/strong>\uff1a\u5728 SQL \u67e5\u8be2\u4e2d\uff0cNULL \u503c\u9700\u8981\u7279\u522b\u5904\u7406\uff0c\u4e0d\u80fd\u76f4\u63a5\u4f7f\u7528\u5e38\u89c4\u7684\u6bd4\u8f83\u8fd0\u7b97\u7b26\uff08\u4f8b\u5982 <code>=<\/code>\uff09\u3002\u5fc5\u987b\u4f7f\u7528 <code>IS NULL<\/code> \u6216 <code>IS NOT NULL<\/code> \u8fdb\u884c\u67e5\u8be2\u3002<\/li>\n\n\n\n<li><strong>\u5e94\u7528\u573a\u666f<\/strong>\uff1aNULL \u901a\u5e38\u7528\u4e8e\u90a3\u4e9b\u6570\u636e\u53ef\u80fd\u7f3a\u5931\u7684\u5b57\u6bb5\uff0c\u6bd4\u5982\u7528\u6237\u7684\u53ef\u9009\u4fe1\u606f\uff08\u5982\u4e2d\u95f4\u540d\u3001\u7535\u8bdd\u53f7\u7801\u7b49\uff09\uff0c\u5f53\u6570\u636e\u4e0d\u53ef\u7528\u65f6\u53ef\u4ee5\u4f7f\u7528 NULL\u3002<\/li>\n<\/ul>\n\n\n\n<h4 class=\"wp-block-heading\">2. <strong>\u7a7a\u5b57\u7b26\u4e32 (&#8220;&#8221;)<\/strong>:<\/h4>\n\n\n\n<ol class=\"wp-block-list\"><\/ol>\n\n\n\n<ol class=\"wp-block-list\"><\/ol>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>\u542b\u4e49<\/strong>\uff1a\u8868\u793a\u4e00\u4e2a\u6709\u6548\u7684\u3001\u7a7a\u7684\u503c\u3002\u7a7a\u5b57\u7b26\u4e32\u4e0d\u662f NULL\uff0c\u5b83\u662f\u4e00\u4e2a\u6709\u6548\u7684\u5b57\u7b26\u4e32\u7c7b\u578b\u503c\uff0c\u957f\u5ea6\u4e3a 0\u3002<\/li>\n\n\n\n<li><strong>\u884c\u4e3a<\/strong>\uff1a\u7a7a\u5b57\u7b26\u4e32\u53ef\u4ee5\u76f4\u63a5\u4f7f\u7528\u5e38\u89c4\u7684\u6bd4\u8f83\u8fd0\u7b97\u7b26\uff0c\u4f8b\u5982 <code>= \"\"<\/code> \u6216 <code>!= \"\"<\/code>\u3002\u5b83\u8868\u793a\u5b57\u6bb5\u5df2\u7ecf\u6709\u4e00\u4e2a\u6709\u6548\u503c\uff0c\u53ea\u4e0d\u8fc7\u8fd9\u4e2a\u503c\u4e3a\u7a7a\u3002<\/li>\n\n\n\n<li><strong>\u5e94\u7528\u573a\u666f<\/strong>\uff1a\u7a7a\u5b57\u7b26\u4e32\u901a\u5e38\u7528\u4e8e\u90a3\u4e9b\u5b57\u6bb5\u5fc5\u586b\u4f46\u53ef\u4ee5\u6ca1\u6709\u5185\u5bb9\u7684\u60c5\u51b5\uff0c\u5982\u7528\u6237\u8f93\u5165\u7684\u8bc4\u8bba\u5b57\u6bb5\uff0c\u7528\u6237\u7684\u540d\u5b57\u5b57\u6bb5\u7b49\uff0c\u5982\u679c\u7528\u6237\u4e0d\u63d0\u4f9b\u8f93\u5165\uff0c\u53ef\u4ee5\u5c06\u5176\u8bbe\u7f6e\u4e3a\u7a7a\u5b57\u7b26\u4e32\u3002<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\">\u4e8c\u3001<strong>\u4e3a\u4ec0\u4e48 MySQL \u4e0d\u5efa\u8bae\u4f7f\u7528 NULL \u4f5c\u4e3a\u9ed8\u8ba4\u503c<\/strong><\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>NULL \u5904\u7406\u7684\u590d\u6742\u6027<\/strong>\uff1a\u5f53\u4e00\u4e2a\u5217\u7684\u9ed8\u8ba4\u503c\u662f NULL \u65f6\uff0c\u67e5\u8be2\u65f6\u7ecf\u5e38\u9700\u8981\u8003\u8651 <code>IS NULL<\/code> \u6761\u4ef6\uff0c\u589e\u52a0\u4e86\u67e5\u8be2\u7684\u590d\u6742\u6027\uff0c\u5c24\u5176\u662f\u5bf9\u4e8e\u5927\u89c4\u6a21\u6570\u636e\u7684\u67e5\u8be2\uff0c\u6027\u80fd\u53ef\u80fd\u53d7\u5230\u5f71\u54cd\u3002<\/li>\n\n\n\n<li>\u4e3e\u4f8b\u6765\u8bf4\uff0c\u5f53\u4f7f\u7528 NULL \u4f5c\u4e3a\u9ed8\u8ba4\u503c\u65f6\uff0c\u67e5\u8be2\u53ef\u80fd\u9700\u8981\u989d\u5916\u7684\u903b\u8f91\u6765\u5904\u7406\u7a7a\u503c\uff0c\u6bd4\u5982 <code>SELECT * FROM users WHERE middle_name IS NULL<\/code>\u3002\u5982\u679c\u67e5\u8be2\u4e2d\u9891\u7e41\u6d89\u53ca NULL \u503c\uff0c\u5b83\u7684\u5904\u7406\u53ef\u80fd\u4f1a\u6bd4\u7b80\u5355\u7684 <code>\"\"<\/code>\uff08\u7a7a\u5b57\u7b26\u4e32\uff09\u6216 <code>0<\/code>\uff08\u6570\u5b57\u7c7b\u578b\u7684\u9ed8\u8ba4\u503c\uff09\u66f4\u4e3a\u7e41\u7410\u4e14\u6027\u80fd\u8f83\u4f4e\u3002<\/li>\n\n\n\n<li><strong>\u6570\u636e\u4e00\u81f4\u6027\u95ee\u9898<\/strong>\uff1a\u5982\u679c\u67d0\u4e9b\u5217\u7684\u6570\u636e\u610f\u4e49\u662f\u201c\u5fc5\u586b\u7684\u201d\u800c\u4f7f\u7528 NULL \u503c\u4f5c\u4e3a\u9ed8\u8ba4\u503c\uff0c\u53ef\u80fd\u4f1a\u5bfc\u81f4\u6570\u636e\u7684\u4e00\u81f4\u6027\u95ee\u9898\u3002\u4f8b\u5982\uff0c\u7528\u6237\u7684\u7535\u5b50\u90ae\u4ef6\u5730\u5740\u5b57\u6bb5\u5982\u679c\u4f7f\u7528 NULL \u4f5c\u4e3a\u9ed8\u8ba4\u503c\uff0c\u53ef\u80fd\u4f1a\u5bfc\u81f4\u5f88\u591a\u8bb0\u5f55\u6ca1\u6709\u586b\u5199\u7535\u5b50\u90ae\u4ef6\uff0c\u5f71\u54cd\u7cfb\u7edf\u903b\u8f91\u3002<\/li>\n\n\n\n<li><strong>\u6027\u80fd\u95ee\u9898<\/strong>\uff1a\u67d0\u4e9b\u5b58\u50a8\u5f15\u64ce\uff08\u5982 InnoDB\uff09\u5bf9 NULL \u503c\u7684\u5904\u7406\u4e0d\u5982\u5e38\u89c4\u503c\uff08\u5982\u7a7a\u5b57\u7b26\u4e32\u6216\u96f6\uff09\u9ad8\u6548\u3002\u5c24\u5176\u662f\u6d89\u53ca\u7d22\u5f15\u65f6\uff0cNULL \u503c\u4f1a\u5bfc\u81f4\u7d22\u5f15\u6548\u7387\u8f83\u4f4e\uff0c\u67e5\u8be2\u53d8\u6162\u3002<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\">\u4e09\u3001<strong>\u4e3a\u4ec0\u4e48\u4f7f\u7528\u7a7a\u5b57\u7b26\u4e32\u4f5c\u4e3a\u9ed8\u8ba4\u503c\u66f4\u5408\u9002<\/strong><\/h3>\n\n\n\n<ol class=\"wp-block-list\">\n<li><strong>\u907f\u514d NULL \u7279\u6b8a\u5904\u7406<\/strong>\uff1a<br>\u4f7f\u7528\u7a7a\u5b57\u7b26\u4e32\uff08&#8221;&#8221;\uff09\u4f5c\u4e3a\u9ed8\u8ba4\u503c\u65f6\uff0c\u53ef\u4ee5\u907f\u514d\u5728\u67e5\u8be2\u4e2d\u9891\u7e41\u4f7f\u7528 <code>IS NULL<\/code> \u6765\u5904\u7406 NULL \u503c\uff0c\u4f7f\u5f97 SQL \u67e5\u8be2\u66f4\u52a0\u7b80\u6d01\u4e14\u9ad8\u6548\u3002\u4f8b\u5982\uff0c\u67e5\u8be2\u7a7a\u5b57\u7b26\u4e32\u53ef\u4ee5\u76f4\u63a5\u4f7f\u7528 <code>= ''<\/code>\uff0c\u800c\u67e5\u8be2 NULL \u5fc5\u987b\u4f7f\u7528 <code>IS NULL<\/code>\u3002<\/li>\n\n\n\n<li><strong>\u6570\u636e\u5b8c\u6574\u6027<\/strong>\uff1a<br>\u5982\u679c\u5b57\u6bb5\u672c\u8eab\u662f\u5fc5\u586b\u7684\uff0c\u4f7f\u7528\u7a7a\u5b57\u7b26\u4e32\u4ee3\u66ff NULL \u503c\u53ef\u4ee5\u786e\u4fdd\u6570\u636e\u7684\u4e00\u81f4\u6027\u3002\u6bd4\u5982\uff0c\u5982\u679c\u4e00\u4e2a\u7528\u6237\u540d\u4e0d\u80fd\u4e3a\u7a7a\uff0c\u4f7f\u7528\u7a7a\u5b57\u7b26\u4e32\u4f5c\u4e3a\u9ed8\u8ba4\u503c\u6bd4 NULL \u66f4\u80fd\u8868\u8fbe\u201c\u7a7a\u201d\u6216\u201c\u672a\u586b\u5199\u201d\u7684\u610f\u56fe\u3002<\/li>\n\n\n\n<li><strong>\u6027\u80fd<\/strong>\uff1a<br>\u7a7a\u5b57\u7b26\u4e32\u662f\u4e00\u4e2a\u6709\u6548\u7684\u5b57\u7b26\u4e32\u503c\uff0c\u5b83\u53ef\u4ee5\u6b63\u5e38\u4f7f\u7528\u7d22\u5f15\uff0c\u901a\u5e38\u4e0d\u4f1a\u5bf9\u67e5\u8be2\u6027\u80fd\u4ea7\u751f\u4e0d\u5229\u5f71\u54cd\u3002\u800c NULL \u503c\u5728\u67d0\u4e9b\u5b58\u50a8\u5f15\u64ce\u4e2d\u5bf9\u7d22\u5f15\u7684\u5f71\u54cd\u8f83\u5927\u3002<\/li>\n<\/ol>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>\u603b\u7ed3<\/strong><\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>NULL \u4e0e \u7a7a\u5b57\u7b26\u4e32\u7684\u672c\u8d28\u533a\u522b<\/strong>\uff1aNULL \u8868\u793a\u6570\u636e\u7f3a\u5931\u6216\u672a\u77e5\uff0c\u800c\u7a7a\u5b57\u7b26\u4e32\u662f\u4e00\u4e2a\u6709\u6548\u7684\u5b57\u7b26\u4e32\u503c\uff0c\u8868\u793a\u503c\u4e3a\u7a7a\u4f46\u5df2\u88ab\u586b\u5199\u3002<\/li>\n\n\n\n<li><strong>MySQL \u4e0d\u5efa\u8bae\u4f7f\u7528 NULL \u4f5c\u4e3a\u9ed8\u8ba4\u503c<\/strong>\uff0c\u56e0\u4e3a\u5b83\u4f1a\u589e\u52a0\u67e5\u8be2\u590d\u6742\u6027\u3001\u5f71\u54cd\u6027\u80fd\u3001\u5e76\u53ef\u80fd\u5bfc\u81f4\u6570\u636e\u4e00\u81f4\u6027\u95ee\u9898\u3002\u7a7a\u5b57\u7b26\u4e32\u4f5c\u4e3a\u9ed8\u8ba4\u503c\u5f80\u5f80\u66f4\u5408\u9002\uff0c\u5c24\u5176\u662f\u5728\u5b57\u6bb5\u9700\u8981\u6709\u6548\u503c\u4f46\u5141\u8bb8\u4e3a\u7a7a\u7684\u60c5\u51b5\u4e0b\u3002<\/li>\n\n\n\n<li><strong>\u5b9e\u8df5\u4e2d<\/strong>\uff1a\u5bf9\u4e8e <strong>\u5b57\u7b26\u4e32\u7c7b\u578b<\/strong> \u5b57\u6bb5\uff0c\u5982\u679c\u6ca1\u6709\u63d0\u4f9b\u8f93\u5165\uff0c\u901a\u5e38\u9009\u62e9\u7a7a\u5b57\u7b26\u4e32\u4f5c\u4e3a\u9ed8\u8ba4\u503c\uff1b\u5bf9\u4e8e <strong>\u6570\u5b57\u7c7b\u578b<\/strong> \u5b57\u6bb5\uff0c\u5982\u679c\u6ca1\u6709\u63d0\u4f9b\u8f93\u5165\uff0c\u53ef\u4ee5\u9009\u62e9 0 \u6216\u5176\u4ed6\u5408\u9002\u7684\u9ed8\u8ba4\u503c\uff0c\u800c\u4e0d\u662f NULL\u3002<\/li>\n<\/ul>\n\n\n\n<p>\u8fd9\u4e2a\u95ee\u9898\u6d89\u53ca\u5230\u6570\u636e\u5e93\u8bbe\u8ba1\u548c\u4f18\u5316\u5b9e\u8df5\uff0c\u56e0\u6b64\u7406\u89e3 NULL \u548c\u7a7a\u5b57\u7b26\u4e32\u7684\u533a\u522b\u5bf9\u4e8e\u9ad8\u6548\u3001\u5065\u58ee\u7684\u6570\u636e\u5e93\u8bbe\u8ba1\u81f3\u5173\u91cd\u8981\u3002\u66f4\u591a\u8be6\u7ec6\u5185\u5bb9\u8bf7\u5173\u6ce8\u5176\u4ed6\u76f8\u5173\u6587\u7ae0\uff01<\/p>\n","protected":false},"excerpt":{"rendered":"<p>MySQL \u4e0d\u5efa\u8bae\u4f7f\u7528 NULL \u4f5c\u4e3a\u5217\u7684\u9ed8\u8ba4\u503c \u4e0e NULL \u548c \u7a7a\u5b57\u7b26\u4e32 (&#8220;&#8221;) [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":3701,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[87],"tags":[],"class_list":["post-3700","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-mysql"],"_links":{"self":[{"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/posts\/3700","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/comments?post=3700"}],"version-history":[{"count":1,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/posts\/3700\/revisions"}],"predecessor-version":[{"id":3702,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/posts\/3700\/revisions\/3702"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/media\/3701"}],"wp:attachment":[{"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/media?parent=3700"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/categories?post=3700"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/tags?post=3700"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}