{"id":186238,"date":"2024-11-11T04:15:26","date_gmt":"2024-11-10T20:15:26","guid":{"rendered":"https:\/\/server.hk\/cnblog\/186238\/"},"modified":"2024-11-11T04:15:27","modified_gmt":"2024-11-10T20:15:27","slug":"%e6%95%b8%e6%93%9a%e5%ba%ab%e6%9f%a5%e8%a9%a2%ef%bc%9a%e9%97%9c%e4%bf%82%e4%bb%a3%e6%95%b8%e7%9a%84%e6%87%89%e7%94%a8%e6%96%b9%e6%b3%95%ef%bc%88%e6%95%b8%e6%93%9a%e5%ba%ab%e5%a6%82%e4%bd%95%e7%94%a8","status":"publish","type":"post","link":"https:\/\/server.hk\/cnblog\/186238\/","title":{"rendered":"\u6578\u64da\u5eab\u67e5\u8a62\uff1a\u95dc\u4fc2\u4ee3\u6578\u7684\u61c9\u7528\u65b9\u6cd5\uff08\u6578\u64da\u5eab\u5982\u4f55\u7528\u95dc\u4fc2\u4ee3\u6578\u5b8c\u6210\u67e5\u8a62\uff09"},"content":{"rendered":"<h1 id=\"%e6%95%b8%e6%93%9a%e5%ba%ab%e6%9f%a5%e8%a9%a2%ef%bc%9a%e9%97%9c%e4%bf%82%e4%bb%a3%e6%95%b8%e7%9a%84%e6%87%89%e7%94%a8%e6%96%b9%e6%b3%95-SQQKYyiJjI\">\u6578\u64da\u5eab\u67e5\u8a62\uff1a\u95dc\u4fc2\u4ee3\u6578\u7684\u61c9\u7528\u65b9\u6cd5<\/h1>\n<p>\u5728\u7576\u4eca\u6578\u64da\u9a45\u52d5\u7684\u4e16\u754c\u4e2d\uff0c\u6578\u64da\u5eab\u7684\u67e5\u8a62\u80fd\u529b\u81f3\u95dc\u91cd\u8981\u3002\u95dc\u4fc2\u4ee3\u6578\u4f5c\u70ba\u6578\u64da\u5eab\u67e5\u8a62\u7684\u57fa\u790e\uff0c\u63d0\u4f9b\u4e86\u4e00\u5957\u5f37\u5927\u7684\u5de5\u5177\u4f86\u64cd\u4f5c\u548c\u6aa2\u7d22\u6578\u64da\u3002\u672c\u6587\u5c07\u63a2\u8a0e\u95dc\u4fc2\u4ee3\u6578\u7684\u57fa\u672c\u6982\u5ff5\u53ca\u5176\u5728\u6578\u64da\u5eab\u67e5\u8a62\u4e2d\u7684\u61c9\u7528\u65b9\u6cd5\u3002<\/p>\n<h2 id=\"%e4%bb%80%e9%ba%bc%e6%98%af%e9%97%9c%e4%bf%82%e4%bb%a3%e6%95%b8%ef%bc%9f-SQQKYyiJjI\">\u4ec0\u9ebc\u662f\u95dc\u4fc2\u4ee3\u6578\uff1f<\/h2>\n<p>\u95dc\u4fc2\u4ee3\u6578\u662f\u4e00\u7a2e\u6578\u5b78\u7d50\u69cb\uff0c\u4e3b\u8981\u7528\u65bc\u64cd\u4f5c\u95dc\u4fc2\u6578\u64da\u5eab\u4e2d\u7684\u6578\u64da\u3002\u5b83\u7531\u4e00\u7d44\u904b\u7b97\u7b26\u7d44\u6210\uff0c\u9019\u4e9b\u904b\u7b97\u7b26\u53ef\u4ee5\u7528\u4f86\u5c0d\u6578\u64da\u9032\u884c\u67e5\u8a62\u3001\u63d2\u5165\u3001\u66f4\u65b0\u548c\u522a\u9664\u7b49\u64cd\u4f5c\u3002\u95dc\u4fc2\u4ee3\u6578\u7684\u57fa\u672c\u904b\u7b97\u7b26\u5305\u62ec\uff1a<\/p>\n<ul>\n<li><strong id=\"%e9%81%b8%e6%93%87%ef%bc%88selection%ef%bc%89-SQQKYyiJjI\">\u9078\u64c7\uff08Selection\uff09<\/strong>\uff1a\u5f9e\u95dc\u4fc2\u4e2d\u9078\u64c7\u6eff\u8db3\u7279\u5b9a\u689d\u4ef6\u7684\u5143\u7d44\u3002<\/li>\n<li><strong id=\"%e6%8a%95%e5%bd%b1%ef%bc%88projection%ef%bc%89-SQQKYyiJjI\">\u6295\u5f71\uff08Projection\uff09<\/strong>\uff1a\u5f9e\u95dc\u4fc2\u4e2d\u9078\u64c7\u7279\u5b9a\u7684\u5c6c\u6027\u3002<\/li>\n<li><strong id=\"%e8%81%af%e6%8e%a5%ef%bc%88join%ef%bc%89-SQQKYyiJjI\">\u806f\u63a5\uff08Join\uff09<\/strong>\uff1a\u5c07\u5169\u500b\u6216\u591a\u500b\u95dc\u4fc2\u6839\u64da\u5171\u540c\u5c6c\u6027\u7d50\u5408\u5728\u4e00\u8d77\u3002<\/li>\n<li><strong id=\"%e4%b8%a6%e9%9b%86%ef%bc%88union%ef%bc%89-SQQKYyiJjI\">\u4e26\u96c6\uff08Union\uff09<\/strong>\uff1a\u5c07\u5169\u500b\u95dc\u4fc2\u7684\u5143\u7d44\u5408\u4f75\uff0c\u53bb\u9664\u91cd\u8907\u7684\u5143\u7d44\u3002<\/li>\n<li><strong id=\"%e5%b7%ae%e9%9b%86%ef%bc%88difference%ef%bc%89-SQQKYyiJjI\">\u5dee\u96c6\uff08Difference\uff09<\/strong>\uff1a\u5f9e\u4e00\u500b\u95dc\u4fc2\u4e2d\u522a\u9664\u53e6\u4e00\u500b\u95dc\u4fc2\u4e2d\u7684\u5143\u7d44\u3002<\/li>\n<li><strong id=\"%e7%ac%9b%e5%8d%a1%e7%88%be%e7%a9%8d%ef%bc%88cartesian-product%ef%bc%89-SQQKYyiJjI\">\u7b1b\u5361\u723e\u7a4d\uff08Cartesian Product\uff09<\/strong>\uff1a\u5c07\u5169\u500b\u95dc\u4fc2\u7684\u6240\u6709\u5143\u7d44\u9032\u884c\u7d44\u5408\u3002<\/li>\n<\/ul>\n<h2 id=\"%e9%97%9c%e4%bf%82%e4%bb%a3%e6%95%b8%e7%9a%84%e5%9f%ba%e6%9c%ac%e9%81%8b%e7%ae%97-SQQKYyiJjI\">\u95dc\u4fc2\u4ee3\u6578\u7684\u57fa\u672c\u904b\u7b97<\/h2>\n<h3 id=\"%e9%81%b8%e6%93%87%ef%bc%88selection%ef%bc%89-SQQKYyiJjI\">\u9078\u64c7\uff08Selection\uff09<\/h3>\n<p>\u9078\u64c7\u904b\u7b97\u7b26\u7528\u65bc\u5f9e\u95dc\u4fc2\u4e2d\u9078\u64c7\u6eff\u8db3\u7279\u5b9a\u689d\u4ef6\u7684\u5143\u7d44\u3002\u4f8b\u5982\uff0c\u5047\u8a2d\u6709\u4e00\u500b\u540d\u70ba <code>Employees<\/code> \u7684\u95dc\u4fc2\uff0c\u5305\u542b\u54e1\u5de5\u7684\u59d3\u540d\u548c\u5e74\u9f61\uff0c\u82e5\u8981\u9078\u64c7\u5e74\u9f61\u5927\u65bc30\u7684\u54e1\u5de5\uff0c\u53ef\u4ee5\u4f7f\u7528\u4ee5\u4e0b\u8868\u793a\uff1a<\/p>\n<pre><code>\u03c3(age &gt; 30)(Employees)<\/code><\/pre>\n<h3 id=\"%e6%8a%95%e5%bd%b1%ef%bc%88projection%ef%bc%89-SQQKYyiJjI\">\u6295\u5f71\uff08Projection\uff09<\/h3>\n<p>\u6295\u5f71\u904b\u7b97\u7b26\u7528\u65bc\u9078\u64c7\u95dc\u4fc2\u4e2d\u7684\u7279\u5b9a\u5c6c\u6027\u3002\u5047\u8a2d\u6211\u5011\u53ea\u60f3\u67e5\u770b\u54e1\u5de5\u7684\u59d3\u540d\uff0c\u53ef\u4ee5\u4f7f\u7528\u4ee5\u4e0b\u8868\u793a\uff1a<\/p>\n<pre><code>\u03c0(name)(Employees)<\/code><\/pre>\n<h3 id=\"%e8%81%af%e6%8e%a5%ef%bc%88join%ef%bc%89-SQQKYyiJjI\">\u806f\u63a5\uff08Join\uff09<\/h3>\n<p>\u806f\u63a5\u904b\u7b97\u7b26\u7528\u65bc\u5c07\u5169\u500b\u95dc\u4fc2\u6839\u64da\u5171\u540c\u5c6c\u6027\u7d50\u5408\u5728\u4e00\u8d77\u3002\u4f8b\u5982\uff0c\u5047\u8a2d\u6709\u4e00\u500b\u540d\u70ba <code>Departments<\/code> \u7684\u95dc\u4fc2\uff0c\u5305\u542b\u90e8\u9580\u7684\u540d\u7a31\u548c\u90e8\u9580ID\uff0c\u82e5\u8981\u5c07\u54e1\u5de5\u548c\u90e8\u9580\u4fe1\u606f\u7d50\u5408\uff0c\u53ef\u4ee5\u4f7f\u7528\u4ee5\u4e0b\u8868\u793a\uff1a<\/p>\n<pre><code>Employees \u2a1d Departments ON Employees.dept_id = Departments.id<\/code><\/pre>\n<h3 id=\"%e4%b8%a6%e9%9b%86%ef%bc%88union%ef%bc%89-SQQKYyiJjI\">\u4e26\u96c6\uff08Union\uff09<\/h3>\n<p>\u4e26\u96c6\u904b\u7b97\u7b26\u7528\u65bc\u5408\u4f75\u5169\u500b\u95dc\u4fc2\u7684\u5143\u7d44\u3002\u4f8b\u5982\uff0c\u82e5\u6709\u5169\u500b\u95dc\u4fc2 <code>Employees_A<\/code> \u548c <code>Employees_B<\/code>\uff0c\u53ef\u4ee5\u4f7f\u7528\u4ee5\u4e0b\u8868\u793a\uff1a<\/p>\n<pre><code>Employees_A \u222a Employees_B<\/code><\/pre>\n<h3 id=\"%e5%b7%ae%e9%9b%86%ef%bc%88difference%ef%bc%89-SQQKYyiJjI\">\u5dee\u96c6\uff08Difference\uff09<\/h3>\n<p>\u5dee\u96c6\u904b\u7b97\u7b26\u7528\u65bc\u5f9e\u4e00\u500b\u95dc\u4fc2\u4e2d\u522a\u9664\u53e6\u4e00\u500b\u95dc\u4fc2\u4e2d\u7684\u5143\u7d44\u3002\u4f8b\u5982\uff0c\u82e5\u8981\u5f9e <code>Employees_A<\/code> \u4e2d\u522a\u9664 <code>Employees_B<\/code> \u7684\u5143\u7d44\uff0c\u53ef\u4ee5\u4f7f\u7528\u4ee5\u4e0b\u8868\u793a\uff1a<\/p>\n<pre><code>Employees_A - Employees_B<\/code><\/pre>\n<h3 id=\"%e7%ac%9b%e5%8d%a1%e7%88%be%e7%a9%8d%ef%bc%88cartesian-product%ef%bc%89-SQQKYyiJjI\">\u7b1b\u5361\u723e\u7a4d\uff08Cartesian Product\uff09<\/h3>\n<p>\u7b1b\u5361\u723e\u7a4d\u904b\u7b97\u7b26\u7528\u65bc\u5c07\u5169\u500b\u95dc\u4fc2\u7684\u6240\u6709\u5143\u7d44\u9032\u884c\u7d44\u5408\u3002\u5047\u8a2d\u6709\u5169\u500b\u95dc\u4fc2 <code>A<\/code> \u548c <code>B<\/code>\uff0c\u53ef\u4ee5\u4f7f\u7528\u4ee5\u4e0b\u8868\u793a\uff1a<\/p>\n<pre><code>A \u00d7 B<\/code><\/pre>\n<h2 id=\"%e9%97%9c%e4%bf%82%e4%bb%a3%e6%95%b8%e5%9c%a8%e6%95%b8%e6%93%9a%e5%ba%ab%e6%9f%a5%e8%a9%a2%e4%b8%ad%e7%9a%84%e6%87%89%e7%94%a8-SQQKYyiJjI\">\u95dc\u4fc2\u4ee3\u6578\u5728\u6578\u64da\u5eab\u67e5\u8a62\u4e2d\u7684\u61c9\u7528<\/h2>\n<p>\u95dc\u4fc2\u4ee3\u6578\u7684\u904b\u7b97\u7b26\u53ef\u4ee5\u7528\u65bc\u69cb\u5efa\u8907\u96dc\u7684\u67e5\u8a62\uff0c\u9019\u4e9b\u67e5\u8a62\u53ef\u4ee5\u5728\u95dc\u4fc2\u6578\u64da\u5eab\u4e2d\u57f7\u884c\u3002\u901a\u904e\u5c07\u9019\u4e9b\u57fa\u672c\u904b\u7b97\u7b26\u7d44\u5408\u5728\u4e00\u8d77\uff0c\u4f7f\u7528\u8005\u53ef\u4ee5\u5be6\u73fe\u5404\u7a2e\u67e5\u8a62\u9700\u6c42\u3002\u4f8b\u5982\uff0c\u82e5\u8981\u67e5\u8a62\u6240\u6709\u5e74\u9f61\u5927\u65bc30\u4e14\u5728\u7279\u5b9a\u90e8\u9580\u5de5\u4f5c\u7684\u54e1\u5de5\uff0c\u53ef\u4ee5\u5c07\u9078\u64c7\u548c\u806f\u63a5\u904b\u7b97\u7b26\u7d50\u5408\u4f7f\u7528\uff1a<\/p>\n<pre><code>\u03c3(age &gt; 30)(Employees \u2a1d Departments ON Employees.dept_id = Departments.id)<\/code><\/pre>\n<p>\u9019\u6a23\u7684\u67e5\u8a62\u4e0d\u50c5\u80fd\u5920\u63d0\u9ad8\u6578\u64da\u6aa2\u7d22\u7684\u6548\u7387\uff0c\u9084\u80fd\u5920\u5e6b\u52a9\u4f7f\u7528\u8005\u66f4\u597d\u5730\u7406\u89e3\u6578\u64da\u4e4b\u9593\u7684\u95dc\u4fc2\u3002<\/p>\n<h2 id=\"%e7%b8%bd%e7%b5%90-SQQKYyiJjI\">\u7e3d\u7d50<\/h2>\n<p>\u95dc\u4fc2\u4ee3\u6578\u70ba\u6578\u64da\u5eab\u67e5\u8a62\u63d0\u4f9b\u4e86\u4e00\u7a2e\u5f37\u5927\u7684\u65b9\u6cd5\uff0c\u901a\u904e\u5176\u57fa\u672c\u904b\u7b97\u7b26\uff0c\u4f7f\u7528\u8005\u53ef\u4ee5\u9748\u6d3b\u5730\u64cd\u4f5c\u548c\u6aa2\u7d22\u6578\u64da\u3002\u7121\u8ad6\u662f\u5728\u5b78\u8853\u7814\u7a76\u9084\u662f\u5546\u696d\u61c9\u7528\u4e2d\uff0c\u7406\u89e3\u95dc\u4fc2\u4ee3\u6578\u7684\u57fa\u672c\u6982\u5ff5\u548c\u904b\u7528\u65b9\u6cd5\u90fd\u662f\u81f3\u95dc\u91cd\u8981\u7684\u3002\u5c0d\u65bc\u9700\u8981\u9ad8\u6548\u6578\u64da\u8655\u7406\u7684\u4f01\u696d\u4f86\u8aaa\uff0c\u9078\u64c7\u5408\u9069\u7684\u6578\u64da\u5eab\u89e3\u6c7a\u65b9\u6848\uff0c\u5982<a href=\"https:\/\/server.hk\">\u9999\u6e2fVPS<\/a>\u6216<a href=\"https:\/\/server.hk\">\u96f2\u4f3a\u670d\u5668<\/a>\uff0c\u80fd\u5920\u9032\u4e00\u6b65\u63d0\u5347\u6578\u64da\u7ba1\u7406\u7684\u6548\u7387\u548c\u9748\u6d3b\u6027\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"<p>\u63a2\u7d22\u95dc\u4fc2\u4ee3\u6578\u5728\u6578\u64da\u5eab\u67e5\u8a62\u4e2d\u7684\u61c9\u7528\u65b9\u6cd5\uff0c\u4e86\u89e3\u5982\u4f55\u5229\u7528\u5176\u539f\u5247\u9ad8\u6548\u5b8c\u6210\u6578\u64da\u6aa2\u7d22\u8207\u64cd\u4f5c\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-186238","post","type-post","status-publish","format-standard","hentry","category-database"],"_links":{"self":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/186238","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=186238"}],"version-history":[{"count":1,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/186238\/revisions"}],"predecessor-version":[{"id":186239,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/186238\/revisions\/186239"}],"wp:attachment":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/media?parent=186238"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/categories?post=186238"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/tags?post=186238"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}