{"id":15915,"date":"2024-07-19T02:55:26","date_gmt":"2024-07-18T23:25:26","guid":{"rendered":"https:\/\/www.itpiran.net\/blog\/?p=15915"},"modified":"2024-07-19T02:55:26","modified_gmt":"2024-07-18T23:25:26","slug":"https-www-digitalocean-com-community-conceptual-articles-understanding-sql-constraints","status":"publish","type":"post","link":"https:\/\/www.itpiran.net\/blog\/zh\/tutorials\/https-www-digitalocean-com-community-conceptual-articles-understanding-sql-constraints\/","title":{"rendered":"\u4e86\u89e3 SQL \u7684\u5c40\u9650\u6027"},"content":{"rendered":"<h2 id=\"%d9%85%d9%82%d8%af%d9%85%d9%87\">\u4ecb\u7ecd<\/h2>\n<p>\u5728\u8bbe\u8ba1\u6570\u636e\u5e93\u65f6\uff0c\u6709\u65f6\u60a8\u53ef\u80fd\u9700\u8981\u5bf9\u67d0\u4e9b\u5217\u4e2d\u5141\u8bb8\u7684\u6570\u636e\u8fdb\u884c\u9650\u5236\u3002\u4f8b\u5982\uff0c\u5982\u679c\u60a8\u8981\u521b\u5efa\u4e00\u4e2a\u5b58\u50a8\u6469\u5929\u5927\u697c\u4fe1\u606f\u7684\u8868\uff0c\u60a8\u53ef\u80fd\u5e0c\u671b\u5b58\u50a8\u6bcf\u680b\u5efa\u7b51\u7269\u9ad8\u5ea6\u7684\u5217\u4e0d\u5141\u8bb8\u51fa\u73b0\u8d1f\u503c\u3002.<\/p>\n<p>\u5173\u7cfb\u6570\u636e\u5e93\u7ba1\u7406\u7cfb\u7edf (RDBMS) \u5141\u8bb8\u60a8\u4f7f\u7528\u7ea6\u675f\u6765\u63a7\u5236\u6dfb\u52a0\u5230\u8868\u4e2d\u7684\u6570\u636e\u3002\u7ea6\u675f\u662f\u4e00\u79cd\u7279\u6b8a\u89c4\u5219\uff0c\u5b83\u9002\u7528\u4e8e\u4e00\u4e2a\u6216\u591a\u4e2a\u5217\uff08\u6216\u6574\u4e2a\u8868\uff09\uff0c\u5e76\u901a\u8fc7\u8bed\u53e5\u9650\u5236\u5bf9\u8868\u6570\u636e\u6240\u505a\u7684\u66f4\u6539\u3002 <code>\u63d2\u5165<\/code>\uff0c <code>\u66f4\u65b0<\/code>\uff0c \u6216\u8005 <code>\u5220\u9664<\/code> \u5b83\u6709\u9650\u5236\u3002.<\/p>\n<p>\u672c\u6587\u8be6\u7ec6\u63a2\u8ba8\u4e86\u7ea6\u675f\u7684\u5b9a\u4e49\u53ca\u5176\u5728\u5173\u7cfb\u6570\u636e\u5e93\u7ba1\u7406\u7cfb\u7edf\uff08RDBMS\uff09\u4e2d\u7684\u5e94\u7528\u3002\u6b64\u5916\uff0c\u672c\u6587\u8fd8\u9010\u4e00\u4ecb\u7ecd\u4e86SQL\u6807\u51c6\u4e2d\u5b9a\u4e49\u7684\u4e94\u79cd\u7ea6\u675f\uff0c\u5e76\u89e3\u91ca\u4e86\u76f8\u5e94\u7684\u51fd\u6570\u3002.<\/p>\n<h2 id=\"%d9%85%d8%ad%d8%af%d9%88%d8%af%db%8c%d8%aa-%d9%87%d8%a7-%da%86%db%8c%d8%b3%d8%aa%d8%9f\">\u6709\u54ea\u4e9b\u5c40\u9650\u6027\uff1f<\/h2>\n<p>\u5728 SQL \u4e2d\uff0c\u7ea6\u675f\u662f\u6307\u5e94\u7528\u4e8e\u5217\u6216\u8868\u7684\u4efb\u4f55\u89c4\u5219\uff0c\u7528\u4e8e\u9650\u5236\u53ef\u4ee5\u63d2\u5165\u5230\u5176\u4e2d\u7684\u6570\u636e\u3002\u6bcf\u5f53\u60a8\u5c1d\u8bd5\u6267\u884c\u66f4\u6539\u8868\u4e2d\u5b58\u50a8\u7684\u6570\u636e\u7684\u64cd\u4f5c\uff08\u4f8b\u5982 INSERT\u3001UPDATE \u6216 DELETE \u8bed\u53e5\uff09\u65f6\uff0c\u5173\u7cfb\u6570\u636e\u5e93\u7ba1\u7406\u7cfb\u7edf (RDBMS) \u90fd\u4f1a\u68c0\u67e5\u8be5\u6570\u636e\u662f\u5426\u8fdd\u53cd\u4e86\u73b0\u6709\u7ea6\u675f\uff0c\u5982\u679c\u8fdd\u53cd\uff0c\u5219\u4f1a\u8fd4\u56de\u9519\u8bef\u3002.<\/p>\n<p>\u6570\u636e\u5e93\u7ba1\u7406\u5458\u901a\u5e38\u4f9d\u9760\u7ea6\u675f\u6765\u786e\u4fdd\u6570\u636e\u5e93\u9075\u5faa\u4e00\u7ec4\u9884\u5b9a\u4e49\u7684\u4e1a\u52a1\u89c4\u5219\u3002\u5728\u6570\u636e\u5e93\u7684\u4e0a\u4e0b\u6587\u4e2d\uff0c\u4e1a\u52a1\u89c4\u5219\u662f\u6307\u4f01\u4e1a\u6216\u5176\u4ed6\u7ec4\u7ec7\u9075\u5faa\u7684\u4efb\u4f55\u7b56\u7565\u6216\u6d41\u7a0b\uff0c\u5176\u6570\u636e\u5fc5\u987b\u9075\u5b88\u8fd9\u4e9b\u7b56\u7565\u6216\u6d41\u7a0b\u3002\u4f8b\u5982\uff0c\u5047\u8bbe\u60a8\u6b63\u5728\u6784\u5efa\u4e00\u4e2a\u7528\u4e8e\u8bb0\u5f55\u5ba2\u6237\u5546\u5e97\u5e93\u5b58\u7684\u6570\u636e\u5e93\u3002\u5982\u679c\u5ba2\u6237\u6307\u5b9a\u6bcf\u4e2a\u4ea7\u54c1\u8bb0\u5f55\u5fc5\u987b\u5177\u6709\u552f\u4e00\u7684\u6807\u8bc6\u53f7\uff0c\u60a8\u53ef\u4ee5\u521b\u5efa\u4e00\u4e2a\u5e26\u6709\u552f\u4e00\u7ea6\u675f\u7684\u5217\uff0c\u4ee5\u786e\u4fdd\u8be5\u5217\u4e2d\u6ca1\u6709\u4e24\u4e2a\u6761\u76ee\u662f\u76f8\u540c\u7684\u3002.<\/p>\n<p>\u7ea6\u675f\u5bf9\u4e8e\u7ef4\u62a4\u6570\u636e\u5b8c\u6574\u6027\u4e5f\u5341\u5206\u6709\u7528\u3002\u6570\u636e\u5b8c\u6574\u6027\u662f\u4e00\u4e2a\u5bbd\u6cdb\u7684\u6982\u5ff5\uff0c\u901a\u5e38\u7528\u6765\u63cf\u8ff0\u6570\u636e\u5e93\u4e2d\u6570\u636e\u7684\u6574\u4f53\u51c6\u786e\u6027\u3001\u4e00\u81f4\u6027\u548c\u5408\u7406\u6027\uff0c\u5e76\u6839\u636e\u5176\u5177\u4f53\u5e94\u7528\u573a\u666f\u8fdb\u884c\u5b9a\u4e49\u3002\u6570\u636e\u5e93\u4e2d\u7684\u8868\u901a\u5e38\u76f8\u4e92\u5173\u8054\uff0c\u4e00\u4e2a\u8868\u4e2d\u7684\u5217\u4f9d\u8d56\u4e8e\u53e6\u4e00\u4e2a\u8868\u4e2d\u7684\u503c\u3002\u7531\u4e8e\u6570\u636e\u5f55\u5165\u5e38\u5e38\u5bb9\u6613\u51fa\u73b0\u4eba\u4e3a\u9519\u8bef\uff0c\u7ea6\u675f\u5728\u8fd9\u79cd\u60c5\u51b5\u4e0b\u5c31\u663e\u5f97\u5c24\u4e3a\u91cd\u8981\uff0c\u56e0\u4e3a\u5b83\u4eec\u53ef\u4ee5\u786e\u4fdd\u4efb\u4f55\u9519\u8bef\u5f55\u5165\u7684\u6570\u636e\u90fd\u4e0d\u4f1a\u5f71\u54cd\u8fd9\u4e9b\u5173\u8054\u5173\u7cfb\uff0c\u4ece\u800c\u907f\u514d\u635f\u5bb3\u6570\u636e\u5e93\u6570\u636e\u7684\u5b8c\u6574\u6027\u3002.<\/p>\n<p>\u5047\u8bbe\u60a8\u6b63\u5728\u8bbe\u8ba1\u4e00\u4e2a\u5305\u542b\u4e24\u4e2a\u8868\u7684\u6570\u636e\u5e93\uff1a\u4e00\u4e2a\u8868\u7528\u4e8e\u5217\u51fa\u5b66\u6821\u7684\u5728\u6821\u5b66\u751f\uff0c\u53e6\u4e00\u4e2a\u8868\u7528\u4e8e\u5217\u51fa\u8be5\u6821\u7bee\u7403\u961f\u7684\u6210\u5458\u3002\u60a8\u53ef\u4ee5\u5bf9\u7bee\u7403\u961f\u8868\u4e2d\u7684\u67d0\u4e00\u5217\u5e94\u7528\u5916\u952e\u7ea6\u675f\uff0c\u4f7f\u5176\u5f15\u7528\u5b66\u6821\u8868\u4e2d\u7684\u67d0\u4e00\u5217\u3002\u8fd9\u6837\u5c31\u5efa\u7acb\u4e86\u4e24\u4e2a\u8868\u4e4b\u95f4\u7684\u5173\u7cfb\uff0c\u8981\u6c42\u7403\u961f\u8868\u4e2d\u7684\u6bcf\u4e2a\u6761\u76ee\u90fd\u5fc5\u987b\u5f15\u7528\u5b66\u751f\u8868\u4e2d\u7684\u67d0\u4e2a\u6761\u76ee\u3002.<\/p>\n<p>\u7528\u6237\u5728\u9996\u6b21\u521b\u5efa\u8868\u65f6\u5b9a\u4e49\u7ea6\u675f\uff0c\u4e5f\u53ef\u4ee5\u7a0d\u540e\u4f7f\u7528 ALTER TABLE \u8bed\u53e5\u6dfb\u52a0\u7ea6\u675f\uff0c\u524d\u63d0\u662f\u8fd9\u4e9b\u7ea6\u675f\u4e0d\u4e0e\u8868\u4e2d\u5df2\u6709\u7684\u6570\u636e\u51b2\u7a81\u3002\u521b\u5efa\u7ea6\u675f\u65f6\uff0c\u6570\u636e\u5e93\u7cfb\u7edf\u4f1a\u81ea\u52a8\u4e3a\u5176\u751f\u6210\u4e00\u4e2a\u540d\u79f0\uff0c\u4f46\u5728\u5927\u591a\u6570 SQL \u5b9e\u73b0\u4e2d\uff0c\u60a8\u53ef\u4ee5\u4e3a\u6bcf\u4e2a\u7ea6\u675f\u6dfb\u52a0\u81ea\u5b9a\u4e49\u540d\u79f0\u3002\u8fd9\u4e9b\u540d\u79f0\u7528\u4e8e\u5728\u4fee\u6539\u6216\u5220\u9664\u7ea6\u675f\u65f6\uff0c\u901a\u8fc7 ALTER TABLE \u8bed\u53e5\u5f15\u7528\u8fd9\u4e9b\u7ea6\u675f\u3002.<\/p>\n<p>SQL \u6807\u51c6\u6b63\u5f0f\u5b9a\u4e49\u4e86\u4e94\u79cd\u7ea6\u675f\uff1a<\/p>\n<ul>\n<li>\u4e3b\u952e<\/li>\n<li>\u5916\u952e<\/li>\n<li>\u72ec\u7279\u7684<\/li>\n<li>\u5ba1\u67e5<\/li>\n<li>\u5b83\u4e0d\u662f\u7a7a\u7684\u3002<\/li>\n<\/ul>\n<p>\u73b0\u5728\u4f60\u5df2\u7ecf\u5bf9\u7ea6\u675f\u7684\u4f7f\u7528\u6709\u4e86\u5927\u81f4\u7684\u4e86\u89e3\uff0c\u8ba9\u6211\u4eec\u4ed4\u7ec6\u770b\u770b\u8fd9\u4e94\u4e2a\u7ea6\u675f\u4e2d\u7684\u6bcf\u4e00\u4e2a\u3002.<\/p>\n<h2 id=\"%da%a9%d9%84%db%8c%d8%af-%d8%a7%d9%88%d9%84%db%8c%d9%87\">\u4e3b\u952e<\/h2>\n<p>\u4e3b\u952e\u7ea6\u675f\u8981\u6c42\u7ed9\u5b9a\u5217\u4e2d\u7684\u6bcf\u4e2a\u6761\u76ee\u90fd\u662f\u552f\u4e00\u7684\u4e14\u4e0d\u80fd\u4e3a NULL\uff0c\u4ece\u800c\u5141\u8bb8\u60a8\u4f7f\u7528\u8be5\u5217\u6765\u6807\u8bc6\u8868\u4e2d\u7684\u6bcf\u4e00\u884c\u3002.<\/p>\n<p>\u5728\u5173\u7cfb\u6a21\u578b\u4e2d\uff0c\u952e\u662f\u6307\u8868\u4e2d\u7684\u4e00\u5217\u6216\u4e00\u7ec4\u5217\uff0c\u5176\u4e2d\u6bcf\u4e2a\u503c\u90fd\u4fdd\u8bc1\u552f\u4e00\u4e14\u4e0d\u5305\u542b NULL \u503c\u3002\u4e3b\u952e\u662f\u4e00\u79cd\u7279\u6b8a\u7684\u952e\uff0c\u5176\u503c\u7528\u4e8e\u6807\u8bc6\u8868\u4e2d\u7684\u6bcf\u4e00\u884c\uff0c\u800c\u6784\u6210\u4e3b\u952e\u7684\u5217\u4e5f\u53ef\u4ee5\u7528\u4e8e\u5728\u6570\u636e\u5e93\u7684\u5176\u4ed6\u90e8\u5206\u6807\u8bc6\u8be5\u8868\u3002.<\/p>\n<p>\u8fd9\u662f\u5173\u7cfb\u578b\u6570\u636e\u5e93\u7684\u4e00\u4e2a\u91cd\u8981\u7279\u6027\uff1a\u6709\u4e86\u4e3b\u952e\uff0c\u7528\u6237\u65e0\u9700\u77e5\u9053\u6570\u636e\u5b9e\u9645\u5b58\u50a8\u5728\u54ea\u53f0\u673a\u5668\u4e0a\uff0c\u6570\u636e\u5e93\u7ba1\u7406\u7cfb\u7edf\uff08DBMS\uff09\u5c31\u80fd\u8ddf\u8e2a\u6bcf\u6761\u8bb0\u5f55\u5e76\u6309\u9700\u68c0\u7d22\u3002\u8fd9\u610f\u5473\u7740\u8bb0\u5f55\u6ca1\u6709\u56fa\u5b9a\u7684\u903b\u8f91\u987a\u5e8f\uff0c\u7528\u6237\u53ef\u4ee5\u6309\u7167\u4efb\u610f\u987a\u5e8f\u6216\u901a\u8fc7\u4efb\u610f\u7b5b\u9009\u6761\u4ef6\u68c0\u7d22\u6570\u636e\u3002.<\/p>\n<p>\u5728 SQL \u4e2d\uff0c\u60a8\u53ef\u4ee5\u4f7f\u7528 PRIMARY KEY \u7ea6\u675f\u521b\u5efa\u4e3b\u952e\uff0c\u5b83\u672c\u8d28\u4e0a\u662f UNIQUE \u7ea6\u675f\u548c NOT NULL \u7ea6\u675f\u7684\u7ec4\u5408\u3002\u5b9a\u4e49\u4e3b\u952e\u540e\uff0c\u6570\u636e\u5e93\u7ba1\u7406\u7cfb\u7edf (DBMS) \u4f1a\u81ea\u52a8\u521b\u5efa\u4e00\u4e2a\u4e0e\u5176\u5173\u8054\u7684\u7d22\u5f15\u3002\u7d22\u5f15\u662f\u4e00\u79cd\u6570\u636e\u5e93\u7ed3\u6784\uff0c\u6709\u52a9\u4e8e\u66f4\u5feb\u5730\u4ece\u8868\u4e2d\u68c0\u7d22\u6570\u636e\u3002\u5c31\u50cf\u6559\u79d1\u4e66\u4e2d\u7684\u7d22\u5f15\u4e00\u6837\uff0c\u67e5\u8be2\u53ea\u9700\u68c0\u67e5\u7d22\u5f15\u5217\u4e2d\u7684\u6761\u76ee\u5373\u53ef\u627e\u5230\u76f8\u5173\u503c\u3002\u8fd9\u4f7f\u5f97\u4e3b\u952e\u80fd\u591f\u4f5c\u4e3a\u8868\u4e2d\u6bcf\u4e00\u884c\u7684\u6807\u8bc6\u7b26\u3002.<\/p>\n<p>\u4e00\u4e2a\u8868\u53ea\u80fd\u6709\u4e00\u4e2a\u4e3b\u952e\uff0c\u4f46\u4e0e\u666e\u901a\u952e\u4e00\u6837\uff0c\u4e3b\u952e\u53ef\u4ee5\u7531\u591a\u4e2a\u5217\u7ec4\u6210\u3002\u4e5f\u5c31\u662f\u8bf4\uff0c\u4e3b\u952e\u7684\u4e00\u4e2a\u663e\u8457\u7279\u5f81\u662f\uff0c\u5b83\u4eec\u53ea\u4f7f\u7528\u552f\u4e00\u6807\u8bc6\u8868\u4e2d\u6bcf\u4e00\u884c\u6240\u9700\u7684\u6700\u5c0f\u5c5e\u6027\u96c6\u3002\u4e3a\u4e86\u8bf4\u660e\u8fd9\u4e00\u70b9\uff0c\u5047\u8bbe\u6709\u4e00\u4e2a\u8868\uff0c\u5b83\u4f7f\u7528\u4ee5\u4e0b\u4e09\u5217\u5b58\u50a8\u5b66\u6821\u5b66\u751f\u7684\u4fe1\u606f\uff1a<\/p>\n<ul>\n<li><code>\u5b66\u751f\u8bc1<\/code>\u7528\u4e8e\u5b58\u50a8\u6bcf\u4e2a\u5b66\u751f\u7684\u552f\u4e00\u8bc6\u522b\u53f7\u7801<\/li>\n<li><code>\u540d<\/code>\u7528\u4e8e\u8bb0\u5f55\u6bcf\u4e2a\u5b66\u751f\u7684\u540d\u5b57<\/li>\n<li><code>\u59d3<\/code>\u7528\u4e8e\u8bb0\u5f55\u6bcf\u4f4d\u5b66\u751f\u7684\u59d3\u6c0f<\/li>\n<\/ul>\n<p>\u5b66\u6821\u91cc\u53ef\u80fd\u5b58\u5728\u4e00\u4e9b\u5b66\u751f\u540c\u540d\u7684\u60c5\u51b5\uff0c\u56e0\u6b64\u201cfirstName\u201d\u5217\u4e0d\u9002\u5408\u7528\u4f5c\u4e3b\u952e\u3002\u540c\u6837\u7684\u60c5\u51b5\u4e5f\u9002\u7528\u4e8e\u201clastName\u201d\u5217\u3002\u867d\u7136\u540c\u65f6\u5305\u542b\u201cfirstName\u201d\u548c\u201clastName\u201d\u5217\u7684\u4e3b\u952e\u6216\u8bb8\u53ef\u884c\uff0c\u4f46\u4ecd\u7136\u5b58\u5728\u4e24\u4e2a\u5b66\u751f\u540c\u540d\u540c\u59d3\u7684\u53ef\u80fd\u6027\u3002.<\/p>\n<p>\u7531\u5b66\u751fID\u548c\u540d\u5b57\u6216\u59d3\u6c0f\u5217\u7ec4\u6210\u7684\u4e3b\u952e\u6216\u8bb8\u53ef\u884c\uff0c\u4f46\u7531\u4e8e\u6bcf\u4e2a\u5b66\u751f\u7684ID\u53f7\u90fd\u662f\u552f\u4e00\u7684\uff0c\u56e0\u6b64\u5728\u4e3b\u952e\u4e2d\u5305\u542b\u6bcf\u4e2a\u59d3\u540d\u5217\u662f\u591a\u4f59\u7684\u3002\u6240\u4ee5\uff0c\u5728\u8fd9\u79cd\u60c5\u51b5\u4e0b\uff0c\u80fd\u591f\u8bc6\u522b\u6bcf\u4e00\u884c\u7684\u6700\u5c0f\u5c5e\u6027\u96c6\uff0c\u4e5f\u5c31\u662f\u4f5c\u4e3a\u8868\u4e3b\u952e\u7684\u7406\u60f3\u9009\u62e9\uff0c\u5c31\u662f\u5b66\u751fID\u5217\u3002.<\/p>\n<p>\u5982\u679c\u952e\u7531\u53ef\u89c2\u5bdf\u3001\u53ef\u7528\u7684\u6570\u636e\u6784\u6210\uff08\u5373\u4ee3\u8868\u73b0\u5b9e\u4e16\u754c\u5b9e\u4f53\u3001\u4e8b\u4ef6\u6216\u5c5e\u6027\u7684\u6570\u636e\uff09\uff0c\u5219\u79f0\u4e3a\u81ea\u7136\u952e\u3002\u5982\u679c\u952e\u662f\u5185\u90e8\u751f\u6210\u7684\uff0c\u4e0d\u4ee3\u8868\u6570\u636e\u5e93\u5916\u90e8\u7684\u4efb\u4f55\u4e8b\u7269\uff0c\u5219\u79f0\u4e3a\u4ee3\u7406\u952e\u6216\u4eba\u5de5\u952e\u3002\u4e00\u4e9b\u6570\u636e\u5e93\u7cfb\u7edf\u4e0d\u5efa\u8bae\u4f7f\u7528\u81ea\u7136\u952e\uff0c\u56e0\u4e3a\u5373\u4f7f\u770b\u4f3c\u56fa\u5b9a\u7684\u6570\u636e\u70b9\u4e5f\u53ef\u80fd\u4ee5\u4e0d\u53ef\u9884\u6d4b\u7684\u65b9\u5f0f\u53d1\u751f\u53d8\u5316\u3002.<\/p>\n<h2 id=\"%da%a9%d9%84%db%8c%d8%af-%d8%ae%d8%a7%d8%b1%d8%ac%db%8c\">\u5916\u952e<\/h2>\n<p>\u5916\u952e\u7ea6\u675f\u8981\u6c42\u7ed9\u5b9a\u5217\u4e2d\u7684\u6bcf\u4e2a\u6761\u76ee\u5fc5\u987b\u5df2\u5b58\u5728\u4e8e\u53e6\u4e00\u4e2a\u8868\u7684\u7279\u5b9a\u5217\u4e2d\u3002.<\/p>\n<p>\u5982\u679c\u8981\u5efa\u7acb\u4e24\u4e2a\u8868\u4e4b\u95f4\u7684\u5173\u8054\uff0c\u4e00\u79cd\u65b9\u6cd5\u662f\u5b9a\u4e49\u4e00\u4e2a\u5e26\u6709\u5916\u952e\u7ea6\u675f\u7684\u5916\u952e\u3002\u5916\u952e\u662f\u6307\u4e00\u4e2a\u8868\uff08\u201c\u5b50\u8868\u201d\uff09\u4e2d\u7684\u4e00\u5217\uff0c\u5176\u503c\u6765\u81ea\u53e6\u4e00\u4e2a\u8868\uff08\u201c\u7236\u8868\u201d\uff09\u4e2d\u7684\u67d0\u4e2a\u952e\u3002\u8fd9\u662f\u4e00\u79cd\u8868\u8fbe\u4e24\u4e2a\u8868\u4e4b\u95f4\u5173\u7cfb\u7684\u65b9\u5f0f\uff1a\u5916\u952e\u7ea6\u675f\u8981\u6c42\u5b83\u6240\u6307\u5411\u7684\u5217\u4e2d\u7684\u503c\u5fc5\u987b\u5b58\u5728\u4e8e\u5b83\u6240\u5f15\u7528\u7684\u5217\u4e2d\u3002.<\/p>\n<p>\u4e0b\u56fe\u5c55\u793a\u4e86\u4e24\u4e2a\u8868\u4e4b\u95f4\u7684\u5173\u7cfb\uff1a\u4e00\u4e2a\u8868\u7528\u4e8e\u8bb0\u5f55\u516c\u53f8\u5458\u5de5\u4fe1\u606f\uff0c\u53e6\u4e00\u4e2a\u8868\u7528\u4e8e\u8ddf\u8e2a\u516c\u53f8\u9500\u552e\u60c5\u51b5\u3002\u5728\u672c\u4f8b\u4e2d\uff0c\u5458\u5de5\u8868\u7684\u4e3b\u952e\u88ab\u9500\u552e\u8868\u7684\u5916\u952e\u5f15\u7528\uff1a<\/p>\n<p><img  loading=\"lazy\"  decoding=\"async\"  src=\"data:image\/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABAQMAAAAl21bKAAAAA1BMVEUAAP+KeNJXAAAAAXRSTlMAQObYZgAAAAlwSFlzAAAOxAAADsQBlSsOGwAAAApJREFUCNdjYAAAAAIAAeIhvDMAAAAASUVORK5CYII=\"  alt=\"\"  width=\"1160\"  height=\"840\"  class=\"aligncenter wp-image-15918 size-full pk-lazyload\"  data-pk-sizes=\"auto\"  data-ls-sizes=\"auto, (max-width: 1160px) 100vw, 1160px\"  data-pk-src=\"https:\/\/cdn.itpiran.net\/2024\/07\/19024637\/1-8.png\"  data-pk-srcset=\"https:\/\/cdn.itpiran.net\/2024\/07\/19024637\/1-8.png 1160w, https:\/\/cdn.itpiran.net\/2024\/07\/19024637\/1-8-300x217.png 300w, https:\/\/cdn.itpiran.net\/2024\/07\/19024637\/1-8-1024x742.png 1024w, https:\/\/cdn.itpiran.net\/2024\/07\/19024637\/1-8-768x556.png 768w, https:\/\/cdn.itpiran.net\/2024\/07\/19024637\/1-8-110x80.png 110w, https:\/\/cdn.itpiran.net\/2024\/07\/19024637\/1-8-200x145.png 200w, https:\/\/cdn.itpiran.net\/2024\/07\/19024637\/1-8-380x275.png 380w, https:\/\/cdn.itpiran.net\/2024\/07\/19024637\/1-8-255x185.png 255w, https:\/\/cdn.itpiran.net\/2024\/07\/19024637\/1-8-550x398.png 550w, https:\/\/cdn.itpiran.net\/2024\/07\/19024637\/1-8-800x579.png 800w\" ><\/p>\n<p>\u5982\u679c\u5c1d\u8bd5\u5411\u5b50\u8868\u4e2d\u63d2\u5165\u4e00\u6761\u8bb0\u5f55\uff0c\u4f46\u5916\u952e\u5217\u4e2d\u8f93\u5165\u7684\u503c\u5728\u7236\u8868\u7684\u4e3b\u952e\u4e2d\u4e0d\u5b58\u5728\uff0c\u5219\u63d2\u5165\u8bed\u53e5\u65e0\u6548\u3002\u8fd9\u6709\u52a9\u4e8e\u7ef4\u62a4\u5173\u7cfb\u7ea7\u522b\u7684\u5b8c\u6574\u6027\uff0c\u56e0\u4e3a\u4e24\u4e2a\u8868\u4e2d\u7684\u884c\u59cb\u7ec8\u6b63\u786e\u5173\u8054\u3002.<\/p>\n<p>\u901a\u5e38\u60c5\u51b5\u4e0b\uff0c\u5b50\u8868\u7684\u5916\u952e\u662f\u5176\u7236\u8868\u7684\u4e3b\u952e\uff0c\u4f46\u8fd9\u5e76\u975e\u603b\u662f\u5982\u6b64\u3002\u5728\u5927\u591a\u6570\u5173\u7cfb\u578b\u6570\u636e\u5e93\u7ba1\u7406\u7cfb\u7edf\uff08RDBMS\uff09\u4e2d\uff0c\u7236\u8868\u4e2d\u4efb\u4f55\u5177\u6709\u552f\u4e00\u952e\uff08UNIQUE\uff09\u6216\u4e3b\u952e\uff08PRIMARY KEY\uff09\u7ea6\u675f\u7684\u5217\u90fd\u53ef\u4ee5\u88ab\u5b50\u8868\u7684\u5916\u952e\u5f15\u7528\u3002.<\/p>\n<h2 id=\"%d9%85%d9%86%d8%ad%d8%b5%d8%b1-%d8%a8%d9%81%d8%b1%d8%af\">\u72ec\u7279\u7684<\/h2>\n<p>UNIQUE \u7ea6\u675f\u53ef\u9632\u6b62\u5c06\u4efb\u4f55\u91cd\u590d\u503c\u6dfb\u52a0\u5230\u7ed9\u5b9a\u5217\u4e2d\u3002.<\/p>\n<p>\u987e\u540d\u601d\u4e49\uff0c\u552f\u4e00\u7ea6\u675f\u8981\u6c42\u7ed9\u5b9a\u5217\u4e2d\u7684\u6bcf\u4e2a\u6761\u76ee\u90fd\u5fc5\u987b\u662f\u552f\u4e00\u503c\u3002\u4efb\u4f55\u5c1d\u8bd5\u6dfb\u52a0\u5df2\u5b58\u5728\u4e8e\u8be5\u5217\u4e2d\u7684\u503c\u7684\u64cd\u4f5c\u90fd\u4f1a\u5bfc\u81f4\u9519\u8bef\u3002.<\/p>\n<p>UNIQUE \u7ea6\u675f\u5bf9\u4e8e\u5f3a\u5236\u8868\u4e4b\u95f4\u5efa\u7acb\u4e00\u5bf9\u4e00\u5173\u7cfb\u975e\u5e38\u6709\u7528\u3002\u5982\u524d\u6240\u8ff0\uff0c\u60a8\u53ef\u4ee5\u4f7f\u7528\u5916\u952e\u5728\u4e24\u4e2a\u8868\u4e4b\u95f4\u5efa\u7acb\u5173\u7cfb\uff0c\u4f46\u8868\u4e4b\u95f4\u53ef\u4ee5\u5b58\u5728\u591a\u79cd\u7c7b\u578b\u7684\u5173\u7cfb\uff1a<\/p>\n<ul>\n<li><code><code>\u06cc\u06a9 \u0628\u0647 \u06cc\u06a9<\/code><\/code>\u5982\u679c\u7236\u8868\u4e2d\u7684\u884c\u4e0e\u5b50\u8868\u4e2d\u7684\u552f\u4e00\u4e00\u884c\u76f8\u5bf9\u5e94\uff0c\u5219\u79f0\u8fd9\u4e24\u4e2a\u8868\u5177\u6709\u4e00\u5bf9\u4e00\u5173\u7cfb\u3002.<\/li>\n<li><code>\u4e00\u5bf9\u591a<\/code>\u5728\u591a\u5bf9\u4e00\u7684\u5173\u7cfb\u4e2d\uff0c\u7236\u8868\u4e2d\u7684\u4e00\u884c\u53ef\u4ee5\u4e0e\u5b50\u8868\u4e2d\u7684\u591a\u884c\u76f8\u5173\u8054\uff0c\u4f46\u5b50\u8868\u4e2d\u7684\u6bcf\u4e00\u884c\u53ea\u80fd\u4e0e\u7236\u8868\u4e2d\u7684\u4e00\u884c\u76f8\u5173\u8054\u3002.<\/li>\n<li><code>\u591a\u5c11\uff1f<\/code>\u5982\u679c\u7236\u8868\u4e2d\u7684\u884c\u53ef\u4ee5\u4e0e\u5b50\u8868\u4e2d\u7684\u591a\u884c\u76f8\u5173\u8054\uff0c\u53cd\u4e4b\u4ea6\u7136\uff0c\u5219\u79f0\u4e24\u8005\u5177\u6709\u591a\u5bf9\u591a\u5173\u7cfb\u3002.<\/li>\n<\/ul>\n<p>\u901a\u8fc7\u5411\u5e94\u7528\u4e86\u5916\u952e\u7ea6\u675f\u7684\u5217\u6dfb\u52a0\u552f\u4e00\u7ea6\u675f\uff0c\u53ef\u4ee5\u786e\u4fdd\u7236\u8868\u4e2d\u7684\u6bcf\u4e2a\u6761\u76ee\u5728\u5b50\u8868\u4e2d\u53ea\u51fa\u73b0\u4e00\u6b21\uff0c\u4ece\u800c\u5728\u4e24\u4e2a\u8868\u4e4b\u95f4\u5efa\u7acb\u4e00\u5bf9\u4e00\u7684\u5173\u7cfb\u3002.<\/p>\n<p>\u8bf7\u6ce8\u610f\uff0c\u60a8\u53ef\u4ee5\u5728\u8868\u7ea7\u522b\u548c\u5217\u7ea7\u522b\u5b9a\u4e49 UNIQUE \u7ea6\u675f\u3002\u5728\u8868\u7ea7\u522b\u5b9a\u4e49\u65f6\uff0cUNIQUE \u7ea6\u675f\u53ef\u4ee5\u5e94\u7528\u4e8e\u591a\u4e2a\u5217\u3002\u5728\u8fd9\u79cd\u60c5\u51b5\u4e0b\uff0c\u7ea6\u675f\u4e2d\u7684\u6bcf\u4e2a\u5217\u90fd\u53ef\u4ee5\u6709\u91cd\u590d\u503c\uff0c\u4f46\u6bcf\u4e00\u884c\u5728\u53d7\u7ea6\u675f\u5217\u4e2d\u7684\u503c\u7ec4\u5408\u5fc5\u987b\u662f\u552f\u4e00\u7684\u3002.<\/p>\n<h2 id=\"%d8%a8%d8%b1%d8%b1%d8%b3%db%8c\">\u5ba1\u67e5<\/h2>\n<p>CHECK \u7ea6\u675f\u5b9a\u4e49\u4e86\u5217\u7684\u6761\u4ef6\uff08\u79f0\u4e3a\u8c13\u8bcd\uff09\uff0c\u8f93\u5165\u5230\u8be5\u5217\u4e2d\u7684\u4efb\u4f55\u503c\u90fd\u5fc5\u987b\u6ee1\u8db3\u8be5\u6761\u4ef6\u3002.<\/p>\n<p>CHECK \u7ea6\u675f\u8c13\u8bcd\u7f16\u5199\u6210\u4e00\u4e2a\u8868\u8fbe\u5f0f\uff0c\u5176\u8ba1\u7b97\u7ed3\u679c\u53ef\u80fd\u4e3a TRUE\u3001FALSE \u6216\u672a\u77e5\u3002\u5982\u679c\u60a8\u5c1d\u8bd5\u5728 CHECK \u7ea6\u675f\u4e2d\u8f93\u5165\u4e00\u4e2a\u503c\uff0c\u5e76\u4e14\u8be5\u503c\u5bfc\u81f4\u8bed\u53e5\u7684\u8ba1\u7b97\u7ed3\u679c\u4e3a TRUE \u6216\u672a\u77e5\uff08NULL \u503c\u4f1a\u5bfc\u81f4\u8fd9\u79cd\u60c5\u51b5\uff09\uff0c\u5219\u64cd\u4f5c\u5c06\u6210\u529f\u3002\u4f46\u662f\uff0c\u5982\u679c\u8868\u8fbe\u5f0f\u7684\u8ba1\u7b97\u7ed3\u679c\u4e3a FALSE\uff0c\u5219\u64cd\u4f5c\u5c06\u5931\u8d25\u3002.<\/p>\n<p>CHECK \u8c13\u8bcd\u901a\u5e38\u4f9d\u8d56\u4e8e\u6570\u5b66\u6bd4\u8f83\u8fd0\u7b97\u7b26\uff08\u4f8b\u5982 &lt;\u3001&gt;\u3001&lt;=\u3001OR &gt;=\uff09\u6765\u9650\u5236\u7ed9\u5b9a\u5217\u4e2d\u5141\u8bb8\u7684\u6570\u636e\u8303\u56f4\u3002\u4f8b\u5982\uff0cCHECK \u7ea6\u675f\u7684\u4e00\u4e2a\u5e38\u89c1\u7528\u9014\u662f\u9632\u6b62\u67d0\u4e9b\u5217\u4e2d\u51fa\u73b0\u8d1f\u503c\uff0c\u56e0\u4e3a\u5728\u67d0\u4e9b\u60c5\u51b5\u4e0b\uff0c\u8d1f\u503c\u662f\u4e0d\u5408\u7406\u7684\uff0c\u5982\u4e0b\u4f8b\u6240\u793a\u3002.<\/p>\n<p>\u8fd9\u6761 CREATE TABLE \u8bed\u53e5\u521b\u5efa\u4e86\u4e00\u4e2a\u540d\u4e3a productInfo \u7684\u8868\uff0c\u5176\u4e2d\u5305\u542b\u540d\u79f0\u3001ID \u53f7\u548c\u4ef7\u683c\u4e09\u5217\uff0c\u5206\u522b\u5b58\u50a8\u6bcf\u4e2a\u4ea7\u54c1\u7684\u540d\u79f0\u3001ID \u53f7\u548c\u4ef7\u683c\u3002\u7531\u4e8e\u4ea7\u54c1\u4ef7\u683c\u4e0d\u53ef\u80fd\u4e3a\u8d1f\u6570\uff0c\u56e0\u6b64\u8be5\u8bed\u53e5\u5bf9\u4ef7\u683c\u5217\u5e94\u7528\u4e86 CHECK \u7ea6\u675f\uff0c\u4ee5\u786e\u4fdd\u5176\u503c\u5747\u4e3a\u6b63\u6570\uff1a<\/p>\n<div class=\"hcb_wrap\" data-no-translation=\"\" data-no-auto-translation=\"\">\n<pre class=\"prism line-numbers lang-sql\" data-lang=\"SQL\"><code>CREATE TABLE productInfo (\r\nproductID int,\r\nname varchar(30),\r\nprice decimal(4,2)\r\nCHECK (price &gt; 0)\r\n);<\/code><\/pre>\n<\/div>\n<p>\u6bcf\u4e2a CHECK \u8c13\u8bcd\u90fd\u4e0d\u80fd\u4f7f\u7528\u6570\u5b66\u6bd4\u8f83\u8fd0\u7b97\u7b26\u3002\u901a\u5e38\uff0c\u60a8\u53ef\u4ee5\u5728 CHECK \u8c13\u8bcd\u4e2d\u4f7f\u7528\u4efb\u4f55\u53ef\u4ee5\u8ba1\u7b97\u7ed3\u679c\u4e3a true\u3001false \u6216 unknown \u7684 SQL \u8fd0\u7b97\u7b26\uff0c\u5305\u62ec LIKE\u3001BETWEEN\u3001IS NOT NULL \u7b49\u3002\u67d0\u4e9b SQL \u5b9e\u73b0\uff08\u4f46\u5e76\u975e\u6240\u6709\u5b9e\u73b0\uff09\u751a\u81f3\u5141\u8bb8\u60a8\u5728 CHECK \u8c13\u8bcd\u4e2d\u5305\u542b\u5b50\u67e5\u8be2\u3002\u4f46\u662f\u8bf7\u6ce8\u610f\uff0c\u5927\u591a\u6570\u5b9e\u73b0\u4e0d\u5141\u8bb8\u60a8\u5728\u8bed\u53e5\u4e2d\u5f15\u7528\u53e6\u4e00\u4e2a\u8868\u3002.<\/p>\n<h2 id=\"%d8%aa%d9%87%db%8c-%d9%86%db%8c%d8%b3%d8%aa\">\u5b83\u4e0d\u662f\u7a7a\u7684\u3002<\/h2>\n<p>NOT NULL \u7ea6\u675f\u53ef\u9632\u6b62\u5c06\u4efb\u4f55 NULL \u503c\u6dfb\u52a0\u5230\u7ed9\u5b9a\u5217\u4e2d\u3002.<\/p>\n<p>\u5728\u5927\u591a\u6570 SQL \u5b9e\u73b0\u4e2d\uff0c\u5982\u679c\u60a8\u63d2\u5165\u4e00\u884c\u6570\u636e\u4f46\u6ca1\u6709\u4e3a\u7279\u5b9a\u5217\u6307\u5b9a\u503c\uff0c\u6570\u636e\u5e93\u7cfb\u7edf\u9ed8\u8ba4\u4f1a\u5c06\u7f3a\u5931\u7684\u6570\u636e\u8868\u793a\u4e3a NULL\u3002\u5728 SQL \u4e2d\uff0cNULL \u662f\u4e00\u4e2a\u7279\u6b8a\u7684\u5173\u952e\u5b57\uff0c\u7528\u4e8e\u8868\u793a\u672a\u77e5\u3001\u7f3a\u5931\u6216\u672a\u6307\u5b9a\u7684\u503c\u3002\u4f46\u662f\uff0cNULL \u672c\u8eab\u5e76\u4e0d\u662f\u4e00\u4e2a\u503c\uff0c\u800c\u662f\u4e00\u79cd\u672a\u77e5\u503c\u7684\u72b6\u6001\u3002.<\/p>\n<p>\u4e3a\u4e86\u8bf4\u660e\u8fd9\u79cd\u533a\u522b\uff0c\u5047\u8bbe\u6709\u4e00\u4e2a\u7528\u4e8e\u8ddf\u8e2a\u827a\u4eba\u7ecf\u7eaa\u516c\u53f8\u5ba2\u6237\u7684\u8868\u683c\uff0c\u5176\u4e2d\u5305\u542b\u6bcf\u4e2a\u5ba2\u6237\u7684\u59d3\u540d\uff08\u5305\u62ec\u540d\u5b57\u548c\u59d3\u6c0f\uff09\u3002\u5982\u679c\u5ba2\u6237\u4f7f\u7528\u5355\u4e2a\u540d\u5b57\uff0c\u4f8b\u5982\u201cCher\u201d\u3001\u201cUsher\u201d\u6216\u201cBeyonc\u00e9\u201d\uff0c\u6570\u636e\u5e93\u7ba1\u7406\u5458\u53ef\u80fd\u53ea\u4f1a\u5728\u540d\u5b57\u5217\u4e2d\u8f93\u5165\u4e00\u4e2a\u540d\u5b57\uff0c\u8fd9\u4f1a\u5bfc\u81f4\u6570\u636e\u5e93\u7ba1\u7406\u7cfb\u7edf\uff08DBMS\uff09\u5728\u59d3\u6c0f\u5217\u4e2d\u63d2\u5165 NULL \u503c\u3002\u6570\u636e\u5e93\u5e76\u975e\u771f\u7684\u5c06\u5ba2\u6237\u7684\u59d3\u6c0f\u89c6\u4e3a\u201c\u7a7a\u503c\u201d\uff0c\u800c\u53ea\u662f\u8868\u793a\u8be5\u884c\u59d3\u6c0f\u5217\u7684\u503c\u672a\u77e5\uff0c\u6216\u8005\u8be5\u5b57\u6bb5\u4e0d\u9002\u7528\u4e8e\u8be5\u7279\u5b9a\u8bb0\u5f55\u3002.<\/p>\n<p>\u987e\u540d\u601d\u4e49\uff0cNOT NULL \u7ea6\u675f\u4f1a\u963b\u6b62\u6307\u5b9a\u5217\u4e2d\u7684\u4efb\u4f55\u503c\u4e3a NULL\u3002\u8fd9\u610f\u5473\u7740\uff0c\u5bf9\u4e8e\u4efb\u4f55\u5e26\u6709 NOT NULL \u7ea6\u675f\u7684\u5217\uff0c\u5728\u63d2\u5165\u65b0\u884c\u65f6\u5fc5\u987b\u4e3a\u5176\u6307\u5b9a\u4e00\u4e2a\u503c\u3002\u5426\u5219\uff0cINSERT \u64cd\u4f5c\u5c06\u5931\u8d25\u3002.<\/p>\n<h2 id=\"%d9%86%d8%aa%db%8c%d8%ac%d9%87\">\u7ed3\u679c<\/h2>\n<p>\u5bf9\u4e8e\u4efb\u4f55\u5e0c\u671b\u8bbe\u8ba1\u5177\u6709\u9ad8\u6570\u636e\u5b8c\u6574\u6027\u548c\u5b89\u5168\u6027\u7684\u6570\u636e\u5e93\u7684\u4eba\u6765\u8bf4\uff0c\u7ea6\u675f\u90fd\u662f\u5fc5\u4e0d\u53ef\u5c11\u7684\u5de5\u5177\u3002\u901a\u8fc7\u9650\u5236\u8f93\u5165\u5230\u5217\u4e2d\u7684\u6570\u636e\uff0c\u60a8\u53ef\u4ee5\u786e\u4fdd\u8868\u4e4b\u95f4\u7684\u5173\u7cfb\u5f97\u5230\u6b63\u786e\u7ef4\u62a4\uff0c\u5e76\u4e14\u6570\u636e\u5e93\u9075\u5faa\u5b9a\u4e49\u5176\u7528\u9014\u7684\u4e1a\u52a1\u89c4\u5219\u3002.<\/p>","protected":false},"excerpt":{"rendered":"\u5f15\u8a00 \u5728\u8bbe\u8ba1\u6570\u636e\u5e93\u65f6\uff0c\u6709\u65f6\u60a8\u53ef\u80fd\u9700\u8981\u5bf9\u6570\u636e\u65bd\u52a0\u4e00\u4e9b\u9650\u5236\u2026\u2026","protected":false},"author":1,"featured_media":15916,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_yoast_wpseo_focuskw":"\u062f\u0631\u06a9 \u0645\u062d\u062f\u0648\u062f\u06cc\u062a \u0647\u0627\u06cc SQL","_yoast_wpseo_title":"","_yoast_wpseo_metadesc":"","_yoast_wpseo_canonical":"","_yoast_wpseo_opengraph-description":"","_yoast_wpseo_opengraph-image":"","_yoast_wpseo_twitter-description":"","_yoast_wpseo_twitter-image":"","_yoast_wpseo_focuskeywords":"","_yoast_wpseo_primary_category":"193","footnotes":""},"categories":[193,349],"tags":[403,391],"class_list":{"0":"post-15915","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-tutorials","8":"category-database","9":"tag-data-base","10":"tag-mysql"},"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v27.3 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>\u062f\u0631\u06a9 \u0645\u062d\u062f\u0648\u062f\u06cc\u062a \u0647\u0627\u06cc SQL - \u0628\u0644\u0627\u06af ITPiran<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.itpiran.net\/blog\/zh\/tutorials\/https-www-digitalocean-com-community-conceptual-articles-understanding-sql-constraints\/\" \/>\n<meta property=\"og:locale\" content=\"zh_CN\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"\u062f\u0631\u06a9 \u0645\u062d\u062f\u0648\u062f\u06cc\u062a \u0647\u0627\u06cc SQL - \u0628\u0644\u0627\u06af ITPiran\" \/>\n<meta property=\"og:description\" content=\"\u0645\u0642\u062f\u0645\u0647 \u0647\u0646\u06af\u0627\u0645 \u0637\u0631\u0627\u062d\u06cc \u06cc\u06a9 \u067e\u0627\u06cc\u06af\u0627\u0647 \u062f\u0627\u062f\u0647\u060c \u0645\u0645\u06a9\u0646 \u0627\u0633\u062a \u0645\u0648\u0627\u0642\u0639\u06cc \u067e\u06cc\u0634 \u0628\u06cc\u0627\u06cc\u062f \u06a9\u0647 \u0628\u062e\u0648\u0627\u0647\u06cc\u062f \u0645\u062d\u062f\u0648\u062f\u06cc\u062a \u0647\u0627\u06cc\u06cc \u0628\u0631\u0627\u06cc \u062f\u0627\u062f\u0647 \u0647\u0627\u06cc&hellip;\" \/>\n<meta property=\"og:url\" content=\"https:\/\/www.itpiran.net\/blog\/zh\/tutorials\/https-www-digitalocean-com-community-conceptual-articles-understanding-sql-constraints\/\" \/>\n<meta property=\"og:site_name\" content=\"\u0628\u0644\u0627\u06af ITPiran\" \/>\n<meta property=\"article:published_time\" content=\"2024-07-18T23:25:26+00:00\" \/>\n<meta property=\"og:image\" content=\"https:\/\/cdn.itpiran.net\/2024\/07\/19024037\/sql.jpg\" \/>\n\t<meta property=\"og:image:width\" content=\"1793\" \/>\n\t<meta property=\"og:image:height\" content=\"1110\" \/>\n\t<meta property=\"og:image:type\" content=\"image\/jpeg\" \/>\n<meta name=\"author\" content=\"admin\" \/>\n<meta name=\"twitter:card\" content=\"summary_large_image\" \/>\n<meta name=\"twitter:label1\" content=\"\u4f5c\u8005\" \/>\n\t<meta name=\"twitter:data1\" content=\"admin\" \/>\n\t<meta name=\"twitter:label2\" content=\"\u9884\u8ba1\u9605\u8bfb\u65f6\u95f4\" \/>\n\t<meta name=\"twitter:data2\" content=\"1 \u5206\" \/>\n<script type=\"application\/ld+json\" class=\"yoast-schema-graph\">{\"@context\":\"https:\\\/\\\/schema.org\",\"@graph\":[{\"@type\":\"Article\",\"@id\":\"https:\\\/\\\/www.itpiran.net\\\/blog\\\/tutorials\\\/https-www-digitalocean-com-community-conceptual-articles-understanding-sql-constraints\\\/#article\",\"isPartOf\":{\"@id\":\"https:\\\/\\\/www.itpiran.net\\\/blog\\\/tutorials\\\/https-www-digitalocean-com-community-conceptual-articles-understanding-sql-constraints\\\/\"},\"author\":{\"name\":\"admin\",\"@id\":\"https:\\\/\\\/www.itpiran.net\\\/blog\\\/#\\\/schema\\\/person\\\/04ed27b919baca468a2273f8e4318f81\"},\"headline\":\"\u062f\u0631\u06a9 \u0645\u062d\u062f\u0648\u062f\u06cc\u062a \u0647\u0627\u06cc SQL\",\"datePublished\":\"2024-07-18T23:25:26+00:00\",\"mainEntityOfPage\":{\"@id\":\"https:\\\/\\\/www.itpiran.net\\\/blog\\\/tutorials\\\/https-www-digitalocean-com-community-conceptual-articles-understanding-sql-constraints\\\/\"},\"wordCount\":107,\"commentCount\":0,\"publisher\":{\"@id\":\"https:\\\/\\\/www.itpiran.net\\\/blog\\\/#organization\"},\"image\":{\"@id\":\"https:\\\/\\\/www.itpiran.net\\\/blog\\\/tutorials\\\/https-www-digitalocean-com-community-conceptual-articles-understanding-sql-constraints\\\/#primaryimage\"},\"thumbnailUrl\":\"https:\\\/\\\/cdn.itpiran.net\\\/2024\\\/07\\\/19024037\\\/sql.jpg\",\"keywords\":[\"data base\",\"MySQL\"],\"articleSection\":[\"\u0622\u0645\u0648\u0632\u0634\u06cc\",\"\u067e\u0627\u06cc\u06af\u0627\u0647 \u062f\u0627\u062f\u0647\"],\"inLanguage\":\"zh-Hans\",\"potentialAction\":[{\"@type\":\"CommentAction\",\"name\":\"Comment\",\"target\":[\"https:\\\/\\\/www.itpiran.net\\\/blog\\\/tutorials\\\/https-www-digitalocean-com-community-conceptual-articles-understanding-sql-constraints\\\/#respond\"]}]},{\"@type\":\"WebPage\",\"@id\":\"https:\\\/\\\/www.itpiran.net\\\/blog\\\/tutorials\\\/https-www-digitalocean-com-community-conceptual-articles-understanding-sql-constraints\\\/\",\"url\":\"https:\\\/\\\/www.itpiran.net\\\/blog\\\/tutorials\\\/https-www-digitalocean-com-community-conceptual-articles-understanding-sql-constraints\\\/\",\"name\":\"\u062f\u0631\u06a9 \u0645\u062d\u062f\u0648\u062f\u06cc\u062a \u0647\u0627\u06cc SQL - \u0628\u0644\u0627\u06af ITPiran\",\"isPartOf\":{\"@id\":\"https:\\\/\\\/www.itpiran.net\\\/blog\\\/#website\"},\"primaryImageOfPage\":{\"@id\":\"https:\\\/\\\/www.itpiran.net\\\/blog\\\/tutorials\\\/https-www-digitalocean-com-community-conceptual-articles-understanding-sql-constraints\\\/#primaryimage\"},\"image\":{\"@id\":\"https:\\\/\\\/www.itpiran.net\\\/blog\\\/tutorials\\\/https-www-digitalocean-com-community-conceptual-articles-understanding-sql-constraints\\\/#primaryimage\"},\"thumbnailUrl\":\"https:\\\/\\\/cdn.itpiran.net\\\/2024\\\/07\\\/19024037\\\/sql.jpg\",\"datePublished\":\"2024-07-18T23:25:26+00:00\",\"breadcrumb\":{\"@id\":\"https:\\\/\\\/www.itpiran.net\\\/blog\\\/tutorials\\\/https-www-digitalocean-com-community-conceptual-articles-understanding-sql-constraints\\\/#breadcrumb\"},\"inLanguage\":\"zh-Hans\",\"potentialAction\":[{\"@type\":\"ReadAction\",\"target\":[\"https:\\\/\\\/www.itpiran.net\\\/blog\\\/tutorials\\\/https-www-digitalocean-com-community-conceptual-articles-understanding-sql-constraints\\\/\"]}]},{\"@type\":\"ImageObject\",\"inLanguage\":\"zh-Hans\",\"@id\":\"https:\\\/\\\/www.itpiran.net\\\/blog\\\/tutorials\\\/https-www-digitalocean-com-community-conceptual-articles-understanding-sql-constraints\\\/#primaryimage\",\"url\":\"https:\\\/\\\/cdn.itpiran.net\\\/2024\\\/07\\\/19024037\\\/sql.jpg\",\"contentUrl\":\"https:\\\/\\\/cdn.itpiran.net\\\/2024\\\/07\\\/19024037\\\/sql.jpg\",\"width\":1793,\"height\":1110},{\"@type\":\"BreadcrumbList\",\"@id\":\"https:\\\/\\\/www.itpiran.net\\\/blog\\\/tutorials\\\/https-www-digitalocean-com-community-conceptual-articles-understanding-sql-constraints\\\/#breadcrumb\",\"itemListElement\":[{\"@type\":\"ListItem\",\"position\":1,\"name\":\"Home\",\"item\":\"https:\\\/\\\/www.itpiran.net\\\/blog\\\/\"},{\"@type\":\"ListItem\",\"position\":2,\"name\":\"\u0622\u0645\u0648\u0632\u0634\u06cc\",\"item\":\"https:\\\/\\\/www.itpiran.net\\\/blog\\\/category\\\/tutorials\\\/\"},{\"@type\":\"ListItem\",\"position\":3,\"name\":\"\u062f\u0631\u06a9 \u0645\u062d\u062f\u0648\u062f\u06cc\u062a \u0647\u0627\u06cc SQL\"}]},{\"@type\":\"WebSite\",\"@id\":\"https:\\\/\\\/www.itpiran.net\\\/blog\\\/#website\",\"url\":\"https:\\\/\\\/www.itpiran.net\\\/blog\\\/\",\"name\":\"\u0628\u0644\u0627\u06af ITPiran\",\"description\":\"\u0627\u062e\u0628\u0627\u0631 \u0648 \u0645\u0642\u0627\u0644\u0627\u062a \u062a\u062c\u0627\u0631\u062a \u067e\u0627\u06cc\u062f\u0627\u0631 \u0627\u06cc\u0631\u0627\u0646\u06cc\u0627\u0646\",\"publisher\":{\"@id\":\"https:\\\/\\\/www.itpiran.net\\\/blog\\\/#organization\"},\"potentialAction\":[{\"@type\":\"SearchAction\",\"target\":{\"@type\":\"EntryPoint\",\"urlTemplate\":\"https:\\\/\\\/www.itpiran.net\\\/blog\\\/?s={search_term_string}\"},\"query-input\":{\"@type\":\"PropertyValueSpecification\",\"valueRequired\":true,\"valueName\":\"search_term_string\"}}],\"inLanguage\":\"zh-Hans\"},{\"@type\":\"Organization\",\"@id\":\"https:\\\/\\\/www.itpiran.net\\\/blog\\\/#organization\",\"name\":\"\u0628\u0644\u0627\u06af \u062a\u062c\u0627\u0631\u062a \u067e\u0627\u06cc\u062f\u0627\u0631 \u0627\u06cc\u0631\u0627\u0646\u06cc\u0627\u0646\",\"alternateName\":\"ITPIran Blog\",\"url\":\"https:\\\/\\\/www.itpiran.net\\\/blog\\\/\",\"logo\":{\"@type\":\"ImageObject\",\"inLanguage\":\"zh-Hans\",\"@id\":\"https:\\\/\\\/www.itpiran.net\\\/blog\\\/#\\\/schema\\\/logo\\\/image\\\/\",\"url\":\"https:\\\/\\\/cdn.itpiran.net\\\/2023\\\/12\\\/27150508\\\/cropped-ITPIRAN-BLOG-LOGO-2.png\",\"contentUrl\":\"https:\\\/\\\/cdn.itpiran.net\\\/2023\\\/12\\\/27150508\\\/cropped-ITPIRAN-BLOG-LOGO-2.png\",\"width\":512,\"height\":512,\"caption\":\"\u0628\u0644\u0627\u06af \u062a\u062c\u0627\u0631\u062a \u067e\u0627\u06cc\u062f\u0627\u0631 \u0627\u06cc\u0631\u0627\u0646\u06cc\u0627\u0646\"},\"image\":{\"@id\":\"https:\\\/\\\/www.itpiran.net\\\/blog\\\/#\\\/schema\\\/logo\\\/image\\\/\"}},{\"@type\":\"Person\",\"@id\":\"https:\\\/\\\/www.itpiran.net\\\/blog\\\/#\\\/schema\\\/person\\\/04ed27b919baca468a2273f8e4318f81\",\"name\":\"admin\",\"url\":\"https:\\\/\\\/www.itpiran.net\\\/blog\\\/zh\\\/author\\\/admin\\\/\"}]}<\/script>\n<!-- \/ Yoast SEO plugin. -->","yoast_head_json":{"title":"\u4e86\u89e3 SQL \u7684\u5c40\u9650\u6027 - ITPiran \u535a\u5ba2","robots":{"index":"index","follow":"follow","max-snippet":"max-snippet:-1","max-image-preview":"max-image-preview:large","max-video-preview":"max-video-preview:-1"},"canonical":"https:\/\/www.itpiran.net\/blog\/zh\/tutorials\/https-www-digitalocean-com-community-conceptual-articles-understanding-sql-constraints\/","og_locale":"zh_CN","og_type":"article","og_title":"\u062f\u0631\u06a9 \u0645\u062d\u062f\u0648\u062f\u06cc\u062a \u0647\u0627\u06cc SQL - \u0628\u0644\u0627\u06af ITPiran","og_description":"\u0645\u0642\u062f\u0645\u0647 \u0647\u0646\u06af\u0627\u0645 \u0637\u0631\u0627\u062d\u06cc \u06cc\u06a9 \u067e\u0627\u06cc\u06af\u0627\u0647 \u062f\u0627\u062f\u0647\u060c \u0645\u0645\u06a9\u0646 \u0627\u0633\u062a \u0645\u0648\u0627\u0642\u0639\u06cc \u067e\u06cc\u0634 \u0628\u06cc\u0627\u06cc\u062f \u06a9\u0647 \u0628\u062e\u0648\u0627\u0647\u06cc\u062f \u0645\u062d\u062f\u0648\u062f\u06cc\u062a \u0647\u0627\u06cc\u06cc \u0628\u0631\u0627\u06cc \u062f\u0627\u062f\u0647 \u0647\u0627\u06cc&hellip;","og_url":"https:\/\/www.itpiran.net\/blog\/zh\/tutorials\/https-www-digitalocean-com-community-conceptual-articles-understanding-sql-constraints\/","og_site_name":"\u0628\u0644\u0627\u06af ITPiran","article_published_time":"2024-07-18T23:25:26+00:00","og_image":[{"width":1793,"height":1110,"url":"https:\/\/cdn.itpiran.net\/2024\/07\/19024037\/sql.jpg","type":"image\/jpeg"}],"author":"admin","twitter_card":"summary_large_image","twitter_misc":{"\u4f5c\u8005":"admin","\u9884\u8ba1\u9605\u8bfb\u65f6\u95f4":"1 \u5206"},"schema":{"@context":"https:\/\/schema.org","@graph":[{"@type":"Article","@id":"https:\/\/www.itpiran.net\/blog\/tutorials\/https-www-digitalocean-com-community-conceptual-articles-understanding-sql-constraints\/#article","isPartOf":{"@id":"https:\/\/www.itpiran.net\/blog\/tutorials\/https-www-digitalocean-com-community-conceptual-articles-understanding-sql-constraints\/"},"author":{"name":"admin","@id":"https:\/\/www.itpiran.net\/blog\/#\/schema\/person\/04ed27b919baca468a2273f8e4318f81"},"headline":"\u062f\u0631\u06a9 \u0645\u062d\u062f\u0648\u062f\u06cc\u062a \u0647\u0627\u06cc SQL","datePublished":"2024-07-18T23:25:26+00:00","mainEntityOfPage":{"@id":"https:\/\/www.itpiran.net\/blog\/tutorials\/https-www-digitalocean-com-community-conceptual-articles-understanding-sql-constraints\/"},"wordCount":107,"commentCount":0,"publisher":{"@id":"https:\/\/www.itpiran.net\/blog\/#organization"},"image":{"@id":"https:\/\/www.itpiran.net\/blog\/tutorials\/https-www-digitalocean-com-community-conceptual-articles-understanding-sql-constraints\/#primaryimage"},"thumbnailUrl":"https:\/\/cdn.itpiran.net\/2024\/07\/19024037\/sql.jpg","keywords":["data base","MySQL"],"articleSection":["\u0622\u0645\u0648\u0632\u0634\u06cc","\u067e\u0627\u06cc\u06af\u0627\u0647 \u062f\u0627\u062f\u0647"],"inLanguage":"zh-Hans","potentialAction":[{"@type":"CommentAction","name":"Comment","target":["https:\/\/www.itpiran.net\/blog\/tutorials\/https-www-digitalocean-com-community-conceptual-articles-understanding-sql-constraints\/#respond"]}]},{"@type":"WebPage","@id":"https:\/\/www.itpiran.net\/blog\/tutorials\/https-www-digitalocean-com-community-conceptual-articles-understanding-sql-constraints\/","url":"https:\/\/www.itpiran.net\/blog\/tutorials\/https-www-digitalocean-com-community-conceptual-articles-understanding-sql-constraints\/","name":"\u4e86\u89e3 SQL \u7684\u5c40\u9650\u6027 - ITPiran \u535a\u5ba2","isPartOf":{"@id":"https:\/\/www.itpiran.net\/blog\/#website"},"primaryImageOfPage":{"@id":"https:\/\/www.itpiran.net\/blog\/tutorials\/https-www-digitalocean-com-community-conceptual-articles-understanding-sql-constraints\/#primaryimage"},"image":{"@id":"https:\/\/www.itpiran.net\/blog\/tutorials\/https-www-digitalocean-com-community-conceptual-articles-understanding-sql-constraints\/#primaryimage"},"thumbnailUrl":"https:\/\/cdn.itpiran.net\/2024\/07\/19024037\/sql.jpg","datePublished":"2024-07-18T23:25:26+00:00","breadcrumb":{"@id":"https:\/\/www.itpiran.net\/blog\/tutorials\/https-www-digitalocean-com-community-conceptual-articles-understanding-sql-constraints\/#breadcrumb"},"inLanguage":"zh-Hans","potentialAction":[{"@type":"ReadAction","target":["https:\/\/www.itpiran.net\/blog\/tutorials\/https-www-digitalocean-com-community-conceptual-articles-understanding-sql-constraints\/"]}]},{"@type":"ImageObject","inLanguage":"zh-Hans","@id":"https:\/\/www.itpiran.net\/blog\/tutorials\/https-www-digitalocean-com-community-conceptual-articles-understanding-sql-constraints\/#primaryimage","url":"https:\/\/cdn.itpiran.net\/2024\/07\/19024037\/sql.jpg","contentUrl":"https:\/\/cdn.itpiran.net\/2024\/07\/19024037\/sql.jpg","width":1793,"height":1110},{"@type":"BreadcrumbList","@id":"https:\/\/www.itpiran.net\/blog\/tutorials\/https-www-digitalocean-com-community-conceptual-articles-understanding-sql-constraints\/#breadcrumb","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https:\/\/www.itpiran.net\/blog\/"},{"@type":"ListItem","position":2,"name":"\u0622\u0645\u0648\u0632\u0634\u06cc","item":"https:\/\/www.itpiran.net\/blog\/category\/tutorials\/"},{"@type":"ListItem","position":3,"name":"\u062f\u0631\u06a9 \u0645\u062d\u062f\u0648\u062f\u06cc\u062a \u0647\u0627\u06cc SQL"}]},{"@type":"WebSite","@id":"https:\/\/www.itpiran.net\/blog\/#website","url":"https:\/\/www.itpiran.net\/blog\/","name":"ITPiran\u535a\u5ba2","description":"\u4f0a\u6717\u53ef\u6301\u7eed\u8d38\u6613\u65b0\u95fb\u548c\u6587\u7ae0","publisher":{"@id":"https:\/\/www.itpiran.net\/blog\/#organization"},"potentialAction":[{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https:\/\/www.itpiran.net\/blog\/?s={search_term_string}"},"query-input":{"@type":"PropertyValueSpecification","valueRequired":true,"valueName":"search_term_string"}}],"inLanguage":"zh-Hans"},{"@type":"Organization","@id":"https:\/\/www.itpiran.net\/blog\/#organization","name":"\u4f0a\u6717\u53ef\u6301\u7eed\u5546\u4e1a\u535a\u5ba2","alternateName":"ITPIran Blog","url":"https:\/\/www.itpiran.net\/blog\/","logo":{"@type":"ImageObject","inLanguage":"zh-Hans","@id":"https:\/\/www.itpiran.net\/blog\/#\/schema\/logo\/image\/","url":"https:\/\/cdn.itpiran.net\/2023\/12\/27150508\/cropped-ITPIRAN-BLOG-LOGO-2.png","contentUrl":"https:\/\/cdn.itpiran.net\/2023\/12\/27150508\/cropped-ITPIRAN-BLOG-LOGO-2.png","width":512,"height":512,"caption":"\u0628\u0644\u0627\u06af \u062a\u062c\u0627\u0631\u062a \u067e\u0627\u06cc\u062f\u0627\u0631 \u0627\u06cc\u0631\u0627\u0646\u06cc\u0627\u0646"},"image":{"@id":"https:\/\/www.itpiran.net\/blog\/#\/schema\/logo\/image\/"}},{"@type":"Person","@id":"https:\/\/www.itpiran.net\/blog\/#\/schema\/person\/04ed27b919baca468a2273f8e4318f81","name":"\u884c\u653f","url":"https:\/\/www.itpiran.net\/blog\/zh\/author\/admin\/"}]}},"_links":{"self":[{"href":"https:\/\/www.itpiran.net\/blog\/zh\/wp-json\/wp\/v2\/posts\/15915","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.itpiran.net\/blog\/zh\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.itpiran.net\/blog\/zh\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.itpiran.net\/blog\/zh\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.itpiran.net\/blog\/zh\/wp-json\/wp\/v2\/comments?post=15915"}],"version-history":[{"count":2,"href":"https:\/\/www.itpiran.net\/blog\/zh\/wp-json\/wp\/v2\/posts\/15915\/revisions"}],"predecessor-version":[{"id":15919,"href":"https:\/\/www.itpiran.net\/blog\/zh\/wp-json\/wp\/v2\/posts\/15915\/revisions\/15919"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.itpiran.net\/blog\/zh\/wp-json\/wp\/v2\/media\/15916"}],"wp:attachment":[{"href":"https:\/\/www.itpiran.net\/blog\/zh\/wp-json\/wp\/v2\/media?parent=15915"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.itpiran.net\/blog\/zh\/wp-json\/wp\/v2\/categories?post=15915"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.itpiran.net\/blog\/zh\/wp-json\/wp\/v2\/tags?post=15915"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}