{"id":196482,"date":"2024-11-13T23:57:23","date_gmt":"2024-11-13T15:57:23","guid":{"rendered":"https:\/\/server.hk\/cnblog\/196482\/"},"modified":"2024-11-13T23:57:24","modified_gmt":"2024-11-13T15:57:24","slug":"%e7%bd%ae%ef%bc%9f%e5%a6%82%e4%bd%95%e8%99%95%e7%90%86%e6%95%b8%e6%93%9a%e5%ba%ab%e4%b8%ad%e7%9a%84null%e5%80%bc%ef%bc%9f-%e6%95%b8%e6%93%9a%e5%ba%abnull%e5%80%bc%e6%80%8e%e9%ba%bc%e8%a8%ad","status":"publish","type":"post","link":"https:\/\/server.hk\/cnblog\/196482\/","title":{"rendered":"\u7f6e\uff1f\u5982\u4f55\u8655\u7406\u6578\u64da\u5eab\u4e2d\u7684Null\u503c\uff1f (\u6578\u64da\u5eabnull\u503c\u600e\u9ebc\u8a2d)"},"content":{"rendered":"<h1 id=\"%e7%bd%ae%ef%bc%9f%e5%a6%82%e4%bd%95%e8%99%95%e7%90%86%e6%95%b8%e6%93%9a%e5%ba%ab%e4%b8%ad%e7%9a%84null%e5%80%bc%ef%bc%9f-%e6%95%b8%e6%93%9a%e5%ba%abnull%e5%80%bc%e6%80%8e%e9%ba%bc%e8%a8%ad-oBROYKOmgA\">\u7f6e\uff1f\u5982\u4f55\u8655\u7406\u6578\u64da\u5eab\u4e2d\u7684Null\u503c\uff1f (\u6578\u64da\u5eabnull\u503c\u600e\u9ebc\u8a2d)<\/h1>\n<p>\u5728\u6578\u64da\u5eab\u8a2d\u8a08\u4e2d\uff0cNull\u503c\u662f\u4e00\u500b\u5e38\u898b\u7684\u6982\u5ff5\uff0c\u4ee3\u8868\u8457\u7f3a\u5931\u6216\u672a\u77e5\u7684\u6578\u64da\u3002\u7406\u89e3Null\u503c\u7684\u610f\u7fa9\u53ca\u5176\u8655\u7406\u65b9\u5f0f\u5c0d\u65bc\u6578\u64da\u5eab\u7684\u5b8c\u6574\u6027\u548c\u67e5\u8a62\u6548\u7387\u81f3\u95dc\u91cd\u8981\u3002\u672c\u6587\u5c07\u63a2\u8a0eNull\u503c\u7684\u5b9a\u7fa9\u3001\u4f7f\u7528\u5834\u666f\u4ee5\u53ca\u5982\u4f55\u5728\u6578\u64da\u5eab\u4e2d\u6b63\u78ba\u8a2d\u7f6e\u548c\u8655\u7406Null\u503c\u3002<\/p>\n<h2 id=\"%e4%bb%80%e9%ba%bc%e6%98%afnull%e5%80%bc%ef%bc%9f-oBROYKOmgA\">\u4ec0\u9ebc\u662fNull\u503c\uff1f<\/h2>\n<p>Null\u503c\u5728\u6578\u64da\u5eab\u4e2d\u8868\u793a\u4e00\u500b\u5b57\u6bb5\u7684\u503c\u662f\u672a\u77e5\u7684\u6216\u4e0d\u5b58\u5728\u7684\u3002\u9019\u8207\u7a7a\u5b57\u7b26\u4e32\u6216\u96f6\u4e0d\u540c\uff0c\u56e0\u70ba\u7a7a\u5b57\u7b26\u4e32\u548c\u96f6\u662f\u5177\u9ad4\u7684\u503c\uff0c\u800cNull\u5247\u8868\u793a\u7f3a\u4e4f\u503c\u3002\u8209\u4f8b\u4f86\u8aaa\uff0c\u5728\u4e00\u500b\u7528\u6236\u8cc7\u6599\u8868\u4e2d\uff0c\u5982\u679c\u67d0\u500b\u7528\u6236\u7684\u96fb\u8a71\u865f\u78bc\u5c1a\u672a\u63d0\u4f9b\uff0c\u5247\u8a72\u5b57\u6bb5\u53ef\u4ee5\u8a2d\u7f6e\u70baNull\u3002<\/p>\n<h2 id=\"null%e5%80%bc%e7%9a%84%e4%bd%bf%e7%94%a8%e5%a0%b4%e6%99%af-oBROYKOmgA\">Null\u503c\u7684\u4f7f\u7528\u5834\u666f<\/h2>\n<ul>\n<li><strong>\u53ef\u9078\u5b57\u6bb5\uff1a<\/strong>\u5728\u67d0\u4e9b\u60c5\u6cc1\u4e0b\uff0c\u67d0\u4e9b\u5b57\u6bb5\u53ef\u80fd\u4e0d\u662f\u6bcf\u500b\u8a18\u9304\u90fd\u9700\u8981\u7684\u3002\u4f8b\u5982\uff0c\u4f7f\u7528\u8005\u7684\u4e2d\u9593\u540d\u53ef\u80fd\u4e0d\u662f\u5fc5\u586b\u9805\uff0c\u9019\u6642\u53ef\u4ee5\u5c07\u5176\u8a2d\u7f6e\u70baNull\u3002<\/li>\n<li><strong>\u7f3a\u5931\u6578\u64da\uff1a<\/strong>\u5728\u6578\u64da\u6536\u96c6\u904e\u7a0b\u4e2d\uff0c\u67d0\u4e9b\u6578\u64da\u53ef\u80fd\u56e0\u70ba\u5404\u7a2e\u539f\u56e0\u800c\u7f3a\u5931\uff0c\u9019\u6642\u53ef\u4ee5\u4f7f\u7528Null\u4f86\u8868\u793a\u9019\u4e9b\u7f3a\u5931\u7684\u6578\u64da\u3002<\/li>\n<li><strong>\u672a\u5b9a\u7fa9\u7684\u72c0\u614b\uff1a<\/strong>\u5728\u67d0\u4e9b\u696d\u52d9\u908f\u8f2f\u4e2d\uff0c\u67d0\u4e9b\u72c0\u614b\u53ef\u80fd\u5c1a\u672a\u5b9a\u7fa9\uff0c\u9019\u6642\u4e5f\u53ef\u4ee5\u4f7f\u7528Null\u4f86\u8868\u793a\u3002<\/li>\n<\/ul>\n<h2 id=\"%e5%a6%82%e4%bd%95%e5%9c%a8%e6%95%b8%e6%93%9a%e5%ba%ab%e4%b8%ad%e8%a8%ad%e7%bd%aenull%e5%80%bc-oBROYKOmgA\">\u5982\u4f55\u5728\u6578\u64da\u5eab\u4e2d\u8a2d\u7f6eNull\u503c<\/h2>\n<p>\u5728\u8a2d\u8a08\u6578\u64da\u5eab\u6642\uff0c\u53ef\u4ee5\u901a\u904e\u4ee5\u4e0b\u65b9\u5f0f\u8a2d\u7f6eNull\u503c\uff1a<\/p>\n<h3 id=\"1-%e5%9c%a8%e5%89%b5%e5%bb%ba%e8%a1%a8%e6%99%82%e8%a8%ad%e7%bd%ae-oBROYKOmgA\">1. \u5728\u5275\u5efa\u8868\u6642\u8a2d\u7f6e<\/h3>\n<p>\u5728\u5275\u5efa\u6578\u64da\u8868\u6642\uff0c\u53ef\u4ee5\u4f7f\u7528SQL\u8a9e\u53e5\u4f86\u6307\u5b9a\u67d0\u4e9b\u5b57\u6bb5\u53ef\u4ee5\u63a5\u53d7Null\u503c\u3002\u4f8b\u5982\uff1a<\/p>\n<pre><code>CREATE TABLE Users (\n    UserID INT PRIMARY KEY,\n    FirstName VARCHAR(50) NOT NULL,\n    LastName VARCHAR(50) NOT NULL,\n    PhoneNumber VARCHAR(15) NULL\n);<\/code><\/pre>\n<p>\u5728\u9019\u500b\u4f8b\u5b50\u4e2d\uff0cPhoneNumber\u5b57\u6bb5\u88ab\u8a2d\u7f6e\u70baNULL\uff0c\u8868\u793a\u9019\u500b\u5b57\u6bb5\u662f\u53ef\u9078\u7684\u3002<\/p>\n<h3 id=\"2-%e6%9b%b4%e6%96%b0%e7%8f%be%e6%9c%89%e8%a8%98%e9%8c%84-oBROYKOmgA\">2. \u66f4\u65b0\u73fe\u6709\u8a18\u9304<\/h3>\n<p>\u5982\u679c\u9700\u8981\u5c07\u67d0\u500b\u5b57\u6bb5\u7684\u503c\u8a2d\u7f6e\u70baNull\uff0c\u53ef\u4ee5\u4f7f\u7528UPDATE\u8a9e\u53e5\u3002\u4f8b\u5982\uff1a<\/p>\n<pre><code>UPDATE Users\nSET PhoneNumber = NULL\nWHERE UserID = 1;<\/code><\/pre>\n<h3 id=\"3-%e6%9f%a5%e8%a9%a2null%e5%80%bc-oBROYKOmgA\">3. \u67e5\u8a62Null\u503c<\/h3>\n<p>\u5728\u67e5\u8a62\u6578\u64da\u6642\uff0c\u6aa2\u67e5Null\u503c\u9700\u8981\u4f7f\u7528IS NULL\u6216IS NOT NULL\u3002\u4f8b\u5982\uff1a<\/p>\n<pre><code>SELECT * FROM Users\nWHERE PhoneNumber IS NULL;<\/code><\/pre>\n<h2 id=\"%e8%99%95%e7%90%86null%e5%80%bc%e7%9a%84%e6%b3%a8%e6%84%8f%e4%ba%8b%e9%a0%85-oBROYKOmgA\">\u8655\u7406Null\u503c\u7684\u6ce8\u610f\u4e8b\u9805<\/h2>\n<p>\u5728\u8655\u7406Null\u503c\u6642\uff0c\u6709\u5e7e\u500b\u6ce8\u610f\u4e8b\u9805\u9700\u8981\u8003\u616e\uff1a<\/p>\n<ul>\n<li><strong>\u907f\u514d\u4f7f\u7528Null\u9032\u884c\u8a08\u7b97\uff1a<\/strong>\u5728\u6578\u5b78\u904b\u7b97\u4e2d\uff0cNull\u503c\u6703\u5c0e\u81f4\u7d50\u679c\u70baNull\uff0c\u56e0\u6b64\u5728\u9032\u884c\u8a08\u7b97\u6642\u9700\u8981\u7279\u5225\u5c0f\u5fc3\u3002<\/li>\n<li><strong>\u4f7f\u7528COALESCE\u51fd\u6578\uff1a<\/strong>\u5728\u67e5\u8a62\u4e2d\uff0c\u53ef\u4ee5\u4f7f\u7528COALESCE\u51fd\u6578\u4f86\u66ff\u4ee3Null\u503c\u3002\u4f8b\u5982\uff1a<\/li>\n<pre><code>SELECT COALESCE(PhoneNumber, '\u672a\u63d0\u4f9b') AS PhoneNumber\nFROM Users;<\/code><\/pre>\n<li><strong>\u8003\u616e\u6578\u64da\u5b8c\u6574\u6027\uff1a<\/strong>\u5728\u8a2d\u8a08\u6578\u64da\u5eab\u6642\uff0c\u61c9\u8003\u616e\u54ea\u4e9b\u5b57\u6bb5\u61c9\u8a72\u5141\u8a31Null\u503c\uff0c\u54ea\u4e9b\u5b57\u6bb5\u61c9\u8a72\u662f\u5fc5\u586b\u7684\uff0c\u4ee5\u78ba\u4fdd\u6578\u64da\u7684\u5b8c\u6574\u6027\u3002<\/li>\n<\/ul>\n<h2 id=\"%e7%b8%bd%e7%b5%90-oBROYKOmgA\">\u7e3d\u7d50<\/h2>\n<p>Null\u503c\u5728\u6578\u64da\u5eab\u4e2d\u662f\u4e00\u500b\u91cd\u8981\u7684\u6982\u5ff5\uff0c\u6b63\u78ba\u5730\u8a2d\u7f6e\u548c\u8655\u7406Null\u503c\u53ef\u4ee5\u63d0\u9ad8\u6578\u64da\u7684\u5b8c\u6574\u6027\u548c\u67e5\u8a62\u6548\u7387\u3002\u5728\u8a2d\u8a08\u6578\u64da\u5eab\u6642\uff0c\u61c9\u6839\u64da\u696d\u52d9\u9700\u6c42\u5408\u7406\u9078\u64c7\u54ea\u4e9b\u5b57\u6bb5\u53ef\u4ee5\u70baNull\uff0c\u4e26\u5728\u67e5\u8a62\u548c\u66f4\u65b0\u6642\u8b39\u614e\u8655\u7406\u3002\u5c0d\u65bc\u9700\u8981\u9ad8\u6548\u6578\u64da\u7ba1\u7406\u7684\u7528\u6236\uff0c\u9078\u64c7\u5408\u9069\u7684 <a href=\"https:\/\/server.hk\">VPS<\/a> \u89e3\u6c7a\u65b9\u6848\u53ef\u4ee5\u63d0\u4f9b\u66f4\u597d\u7684\u6027\u80fd\u548c\u9748\u6d3b\u6027\u3002\u4e86\u89e3\u5982\u4f55\u5728\u6578\u64da\u5eab\u4e2d\u6709\u6548\u7ba1\u7406Null\u503c\uff0c\u5c07\u6709\u52a9\u65bc\u63d0\u5347\u6574\u9ad4\u6578\u64da\u8655\u7406\u7684\u8cea\u91cf\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"<p>\u4e86\u89e3\u5982\u4f55\u5728\u6578\u64da\u5eab\u4e2d\u8655\u7406Null\u503c\uff0c\u5b78\u7fd2\u6700\u4f73\u5be6\u8e10\u548c\u6280\u5de7\uff0c\u4ee5\u78ba\u4fdd\u6578\u64da\u5b8c\u6574\u6027\u548c\u67e5\u8a62\u6548\u7387\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-196482","post","type-post","status-publish","format-standard","hentry","category-database"],"_links":{"self":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/196482","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=196482"}],"version-history":[{"count":1,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/196482\/revisions"}],"predecessor-version":[{"id":196483,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/196482\/revisions\/196483"}],"wp:attachment":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/media?parent=196482"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/categories?post=196482"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/tags?post=196482"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}