{"id":5620,"date":"2024-11-14T12:28:40","date_gmt":"2024-11-14T04:28:40","guid":{"rendered":"https:\/\/fwq.ai\/blog\/5620\/"},"modified":"2024-11-14T12:28:40","modified_gmt":"2024-11-14T04:28:40","slug":"sql%e4%b8%8d%e7%ad%89%e4%ba%8e0%e6%80%8e%e4%b9%88%e8%a1%a8%e7%a4%ba","status":"publish","type":"post","link":"https:\/\/fwq.ai\/blog\/5620\/","title":{"rendered":"sql\u4e0d\u7b49\u4e8e0\u600e\u4e48\u8868\u793a"},"content":{"rendered":"<blockquote><p>\n  \u5728 sql \u4e2d\uff0c\u8868\u793a\u975e\u96f6\u503c\u7684\u56db\u79cd\u65b9\u6cd5\u5305\u62ec\uff1anot null \u7ea6\u675f\u3001\u9ed8\u8ba4\u503c\u3001check \u7ea6\u675f\u548c case \u8868\u8fbe\u5f0f\u3002\u8fd9\u4e9b\u65b9\u6cd5\u53ef\u786e\u4fdd\u5217\u59cb\u7ec8\u5305\u542b\u975e\u96f6\u503c\u6216\u6839\u636e\u5217\u503c\u6761\u4ef6\u8fd4\u56de\u975e\u96f6\u6307\u793a\u5668\u3002\n<\/p><\/blockquote>\n<p><img decoding=\"async\" src=\"https:\/\/img.php.cn\/upload\/article\/202405\/30\/2024053019093777755.jpg\" class=\"aligncenter\" title=\"sql\u4e0d\u7b49\u4e8e0\u600e\u4e48\u8868\u793a\u63d2\u56fe\" alt=\"sql\u4e0d\u7b49\u4e8e0\u600e\u4e48\u8868\u793a\u63d2\u56fe\" \/><\/p>\n<p><strong>SQL \u4e2d\u975e\u96f6\u503c\u7684\u8868\u793a<\/strong><\/p>\n<p>\u5728 SQL \u4e2d\uff0c\u53ef\u4ee5\u4f7f\u7528\u4ee5\u4e0b\u65b9\u6cd5\u6765\u8868\u793a\u975e\u96f6\u503c\uff1a<\/p>\n<ul>\n<li> <strong>NOT NULL \u7ea6\u675f\uff1a<\/strong>\u901a\u8fc7\u5728\u5217\u4e0a\u6dfb\u52a0 NOT NULL \u7ea6\u675f\u6765\u786e\u4fdd\u8be5\u5217\u4e0d\u5141\u8bb8 NULL \u503c\u3002\u8fd9\u79cd\u65b9\u6cd5\u5bf9\u4e8e\u786e\u4fdd\u5217\u59cb\u7ec8\u5305\u542b\u503c\u975e\u5e38\u6709\u7528\u3002<\/li>\n<\/ul>\n<pre>CREATE TABLE my_table (\n  id INT NOT NULL,\n  name VARCHAR(255) NOT NULL\n);<\/pre>\n<p>  \u767b\u5f55\u540e\u590d\u5236   <\/p>\n<ul>\n<li> <strong>DEFAULT \u503c\uff1a<\/strong>\u4e3a\u5217\u6307\u5b9a\u4e00\u4e2a\u9ed8\u8ba4\u503c\uff0c\u5f53\u6ca1\u6709\u660e\u786e\u6307\u5b9a\u503c\u65f6\uff0c\u8be5\u503c\u5c06\u81ea\u52a8\u63d2\u5165\u3002\u8fd9\u6709\u52a9\u4e8e\u786e\u4fdd\u5217\u59cb\u7ec8\u5305\u542b\u4e00\u4e2a\u503c\uff0c\u5373\u4f7f\u8be5\u503c\u4e0d\u662f\u7528\u6237\u63d0\u4f9b\u7684\u3002<\/li>\n<\/ul>\n<pre>CREATE TABLE my_table (\n  id INT NOT NULL,\n  name VARCHAR(255) DEFAULT 'John Doe'\n);<\/pre>\n<p>  \u767b\u5f55\u540e\u590d\u5236   <\/p>\n<ul>\n<li> <strong>\u68c0\u67e5\u7ea6\u675f\uff1a<\/strong>\u4f7f\u7528 CHECK \u7ea6\u675f\u6765\u5b9a\u4e49\u4e00\u4e2a\u6761\u4ef6\uff0c\u8be5\u6761\u4ef6\u5fc5\u987b\u7531\u5217\u503c\u6ee1\u8db3\u3002\u5982\u679c\u6761\u4ef6\u4e0d\u6ee1\u8db3\uff0c\u5219\u4f1a\u5f15\u53d1\u9519\u8bef\u3002<\/li>\n<\/ul>\n<pre>CREATE TABLE my_table (\n  id INT NOT NULL,\n  value INT CHECK (value &gt; 0)\n);<\/pre>\n<p>  \u767b\u5f55\u540e\u590d\u5236   <\/p>\n<ul>\n<li> <strong>SUBSTRING \u51fd\u6570\uff1a<\/strong>\u5bf9\u4e8e\u5b57\u7b26\u4e32\u5217\uff0c\u53ef\u4ee5\u4f7f\u7528 SUBSTRING \u51fd\u6570\u6765\u68c0\u67e5\u5b57\u7b26\u4e32\u662f\u5426\u4e3a\u7a7a\u3002\u5982\u679c\u5b57\u7b26\u4e32\u4e0d\u4e3a\u7a7a\uff0c\u5219\u5176\u957f\u5ea6\u5c06\u5927\u4e8e 0\u3002<\/li>\n<\/ul>\n<pre>SELECT * FROM my_table WHERE SUBSTRING(name, 1, 1) &lt;&gt; '';<\/pre>\n<p>  \u767b\u5f55\u540e\u590d\u5236   <\/p>\n<ul>\n<li> <strong>CASE \u8868\u8fbe\u5f0f\uff1a<\/strong>\u53ef\u4ee5\u4f7f\u7528 CASE \u8868\u8fbe\u5f0f\u6765\u57fa\u4e8e\u5217\u7684\u503c\u8fd4\u56de\u4e0d\u540c\u503c\u3002\u5bf9\u4e8e\u975e\u96f6\u503c\uff0c\u53ef\u4ee5\u8fd4\u56de 1\uff0c\u5426\u5219\u8fd4\u56de 0\u3002<\/li>\n<\/ul>\n<pre>SELECT CASE WHEN value &gt; 0 THEN 1 ELSE 0 END AS is_non_zero FROM my_table;<\/pre>\n<p>  \u767b\u5f55\u540e\u590d\u5236   <\/p>\n<p>\u4ee5\u4e0a\u5c31\u662fsql\u4e0d\u7b49\u4e8e0\u600e\u4e48\u8868\u793a\u7684\u8be6\u7ec6\u5185\u5bb9\uff0c\u66f4\u591a\u8bf7\u5173\u6ce8\u7c73\u4e91\u7f51\u5176\u5b83\u76f8\u5173\u6587\u7ae0\uff01<\/p>\n","protected":false},"excerpt":{"rendered":"<p>\u5728 sql \u4e2d\uff0c\u8868\u793a\u975e\u96f6\u503c\u7684\u56db\u79cd\u65b9\u6cd5\u5305\u62ec\uff1anot null \u7ea6\u675f\u3001\u9ed8\u8ba4\u503c\u3001check \u7ea6\u675f\u548c case \u8868\u8fbe\u5f0f\u3002\u8fd9\u4e9b\u65b9\u6cd5\u53ef\u786e\u4fdd\u5217\u59cb\u7ec8\u5305\u542b\u975e\u96f6\u503c\u6216\u6839\u636e\u5217\u503c\u6761\u4ef6\u8fd4\u56de\u975e\u96f6\u6307\u793a\u5668\u3002 SQL \u4e2d\u975e\u96f6\u503c\u7684\u8868\u793a \u5728 SQL \u4e2d\uff0c\u53ef\u4ee5\u4f7f\u7528\u4ee5\u4e0b\u65b9\u6cd5\u6765\u8868\u793a\u975e\u96f6\u503c\uff1a NOT NULL \u7ea6\u675f\uff1a\u901a\u8fc7\u5728\u5217\u4e0a\u6dfb\u52a0 NOT NULL \u7ea6\u675f\u6765\u786e\u4fdd\u8be5\u5217\u4e0d\u5141\u8bb8 NULL \u503c\u3002\u8fd9\u79cd\u65b9\u6cd5\u5bf9\u4e8e\u786e\u4fdd\u5217\u59cb\u7ec8\u5305\u542b\u503c\u975e\u5e38\u6709\u7528\u3002 CREATE TABLE my_table ( id INT NOT NULL, name VARCHAR(255) NOT NULL ); \u767b\u5f55\u540e\u590d\u5236 DEFAULT \u503c\uff1a\u4e3a\u5217\u6307\u5b9a\u4e00\u4e2a\u9ed8\u8ba4\u503c\uff0c\u5f53\u6ca1\u6709\u660e\u786e\u6307\u5b9a\u503c\u65f6\uff0c\u8be5\u503c\u5c06\u81ea\u52a8\u63d2\u5165\u3002\u8fd9\u6709\u52a9\u4e8e\u786e\u4fdd\u5217\u59cb\u7ec8\u5305\u542b\u4e00\u4e2a\u503c\uff0c\u5373\u4f7f\u8be5\u503c\u4e0d\u662f\u7528\u6237\u63d0\u4f9b\u7684\u3002 CREATE TABLE my_table ( id INT NOT NULL, name VARCHAR(255) DEFAULT &#8216;John Doe&#8217; ); \u767b\u5f55\u540e\u590d\u5236 \u68c0\u67e5\u7ea6\u675f\uff1a\u4f7f\u7528 CHECK \u7ea6\u675f\u6765\u5b9a\u4e49\u4e00\u4e2a\u6761\u4ef6\uff0c\u8be5\u6761\u4ef6\u5fc5\u987b\u7531\u5217\u503c\u6ee1\u8db3\u3002\u5982\u679c\u6761\u4ef6\u4e0d\u6ee1\u8db3\uff0c\u5219\u4f1a\u5f15\u53d1\u9519\u8bef\u3002 [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[16],"tags":[],"class_list":["post-5620","post","type-post","status-publish","format-standard","hentry","category-16"],"_links":{"self":[{"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/posts\/5620","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/comments?post=5620"}],"version-history":[{"count":0,"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/posts\/5620\/revisions"}],"wp:attachment":[{"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/media?parent=5620"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/categories?post=5620"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/tags?post=5620"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}