{"id":163019,"date":"2024-11-04T19:58:17","date_gmt":"2024-11-04T11:58:17","guid":{"rendered":"https:\/\/server.hk\/cnblog\/163019\/"},"modified":"2024-11-04T19:58:18","modified_gmt":"2024-11-04T11:58:18","slug":"%e6%8f%ad%e9%96%8b%e5%8a%9f%e8%83%bd%e5%bc%b7%e5%a4%a7%e7%9a%84%e6%95%b8%e6%93%9a%e5%ba%ab%e8%a1%a8dual%e7%9a%84%e7%a5%9e%e7%a7%98%e9%9d%a2%e7%b4%97","status":"publish","type":"post","link":"https:\/\/server.hk\/cnblog\/163019\/","title":{"rendered":"\u63ed\u958b\u529f\u80fd\u5f37\u5927\u7684\u6578\u64da\u5eab\u8868DUAL\u7684\u795e\u79d8\u9762\u7d17"},"content":{"rendered":"<h1 id=\"%e6%8f%ad%e9%96%8b%e5%8a%9f%e8%83%bd%e5%bc%b7%e5%a4%a7%e7%9a%84%e6%95%b8%e6%93%9a%e5%ba%ab%e8%a1%a8dual%e7%9a%84%e7%a5%9e%e7%a7%98%e9%9d%a2%e7%b4%97-xqbpDHxKEH\">\u63ed\u958b\u529f\u80fd\u5f37\u5927\u7684\u6578\u64da\u5eab\u8868DUAL\u7684\u795e\u79d8\u9762\u7d17<\/h1>\n<p>\u5728\u6578\u64da\u5eab\u7ba1\u7406\u7cfb\u7d71\u4e2d\uff0c\u8868\u683c\u662f\u5b58\u5132\u6578\u64da\u7684\u57fa\u672c\u55ae\u4f4d\uff0c\u800c\u5728Oracle\u6578\u64da\u5eab\u4e2d\uff0c\u6709\u4e00\u500b\u7279\u5225\u7684\u8868\u683c\u540d\u70baDUAL\u3002\u9019\u500b\u8868\u683c\u7684\u5b58\u5728\u5c0d\u65bc\u8a31\u591a\u958b\u767c\u8005\u4f86\u8aaa\u53ef\u80fd\u662f\u500b\u8b0e\uff0c\u4f46\u5b83\u5be6\u969b\u4e0a\u5728\u6578\u64da\u5eab\u64cd\u4f5c\u4e2d\u626e\u6f14\u8457\u91cd\u8981\u7684\u89d2\u8272\u3002\u672c\u6587\u5c07\u6df1\u5165\u63a2\u8a0eDUAL\u8868\u7684\u529f\u80fd\u3001\u7528\u9014\u53ca\u5176\u80cc\u5f8c\u7684\u539f\u7406\u3002<\/p>\n<h2 id=\"%e4%bb%80%e9%ba%bc%e6%98%afdual%e8%a1%a8%ef%bc%9f-xqbpDHxKEH\">\u4ec0\u9ebc\u662fDUAL\u8868\uff1f<\/h2>\n<p>DUAL\u8868\u662f\u4e00\u500b\u7279\u6b8a\u7684\u865b\u64ec\u8868\u683c\uff0c\u4e3b\u8981\u5b58\u5728\u65bcOracle\u6578\u64da\u5eab\u4e2d\u3002\u5b83\u7684\u8a2d\u8a08\u521d\u8877\u662f\u70ba\u4e86\u63d0\u4f9b\u4e00\u500b\u7c21\u55ae\u7684\u65b9\u5f0f\u4f86\u57f7\u884c\u67e5\u8a62\uff0c\u800c\u4e0d\u9700\u8981\u4f9d\u8cf4\u65bc\u5be6\u969b\u7684\u6578\u64da\u8868\u3002DUAL\u8868\u7684\u7d50\u69cb\u975e\u5e38\u7c21\u55ae\uff0c\u901a\u5e38\u53ea\u6709\u4e00\u884c\u4e00\u5217\uff0c\u5217\u540d\u70baDUMMY\uff0c\u4e26\u4e14\u5176\u503c\u70ba&#8217;X&#8217;\u3002<\/p>\n<h3 id=\"dual%e8%a1%a8%e7%9a%84%e7%b5%90%e6%a7%8b-xqbpDHxKEH\">DUAL\u8868\u7684\u7d50\u69cb<\/h3>\n<pre><code>SELECT * FROM DUAL;\n<\/code><\/pre>\n<p>\u57f7\u884c\u4e0a\u8ff0\u67e5\u8a62\u5f8c\uff0c\u8fd4\u56de\u7684\u7d50\u679c\u5982\u4e0b\uff1a<\/p>\n<pre><code>DUMMY\n------\nX\n<\/code><\/pre>\n<h2 id=\"dual%e8%a1%a8%e7%9a%84%e7%94%a8%e9%80%94-xqbpDHxKEH\">DUAL\u8868\u7684\u7528\u9014<\/h2>\n<p>DUAL\u8868\u7684\u4e3b\u8981\u7528\u9014\u662f\u57f7\u884c\u4e0d\u9700\u8981\u5f9e\u5be6\u969b\u8868\u683c\u4e2d\u6aa2\u7d22\u6578\u64da\u7684\u67e5\u8a62\u3002\u4ee5\u4e0b\u662f\u4e00\u4e9b\u5e38\u898b\u7684\u4f7f\u7528\u5834\u666f\uff1a<\/p>\n<ul>\n<li><strong>\u8a08\u7b97\u8868\u9054\u5f0f\uff1a<\/strong>\u53ef\u4ee5\u4f7f\u7528DUAL\u8868\u4f86\u8a08\u7b97\u6578\u5b78\u8868\u9054\u5f0f\uff0c\u4f8b\u5982\uff1a<\/li>\n<\/ul>\n<pre><code>SELECT 1 + 1 FROM DUAL;\n<\/code><\/pre>\n<p>\u9019\u5c07\u8fd4\u56de2\u3002<\/p>\n<ul>\n<li><strong>\u7372\u53d6\u7576\u524d\u65e5\u671f\u548c\u6642\u9593\uff1a<\/strong>DUAL\u8868\u4e5f\u5e38\u7528\u65bc\u7372\u53d6\u7cfb\u7d71\u7684\u7576\u524d\u65e5\u671f\u548c\u6642\u9593\uff1a<\/li>\n<\/ul>\n<pre><code>SELECT SYSDATE FROM DUAL;\n<\/code><\/pre>\n<p>\u9019\u5c07\u8fd4\u56de\u7576\u524d\u7684\u65e5\u671f\u548c\u6642\u9593\u3002<\/p>\n<ul>\n<li><strong>\u57f7\u884c\u51fd\u6578\uff1a<\/strong>\u53ef\u4ee5\u4f7f\u7528DUAL\u8868\u4f86\u8abf\u7528\u5404\u7a2e\u5167\u5efa\u51fd\u6578\uff0c\u4f8b\u5982\uff1a<\/li>\n<\/ul>\n<pre><code>SELECT UPPER('hello') FROM DUAL;\n<\/code><\/pre>\n<p>\u9019\u5c07\u8fd4\u56de&#8217;HELLO&#8217;\u3002<\/p>\n<h2 id=\"dual%e8%a1%a8%e7%9a%84%e7%89%b9%e9%bb%9e-xqbpDHxKEH\">DUAL\u8868\u7684\u7279\u9ede<\/h2>\n<p>DUAL\u8868\u6709\u5e7e\u500b\u986f\u8457\u7684\u7279\u9ede\uff1a<\/p>\n<ul>\n<li><strong>\u865b\u64ec\u6027\uff1a<\/strong>DUAL\u8868\u4e26\u4e0d\u4f54\u7528\u5be6\u969b\u7684\u5b58\u5132\u7a7a\u9593\uff0c\u56e0\u70ba\u5b83\u53ea\u662f\u4e00\u500b\u908f\u8f2f\u8868\u3002<\/li>\n<li><strong>\u55ae\u884c\u55ae\u5217\uff1a<\/strong>DUAL\u8868\u53ea\u6709\u4e00\u884c\u4e00\u5217\uff0c\u9019\u4f7f\u5f97\u5b83\u5728\u57f7\u884c\u7c21\u55ae\u67e5\u8a62\u6642\u975e\u5e38\u9ad8\u6548\u3002<\/li>\n<li><strong>\u81ea\u52d5\u751f\u6210\uff1a<\/strong>\u5728Oracle\u6578\u64da\u5eab\u4e2d\uff0cDUAL\u8868\u662f\u81ea\u52d5\u751f\u6210\u7684\uff0c\u7121\u9700\u7528\u6236\u624b\u52d5\u5275\u5efa\u3002<\/li>\n<\/ul>\n<h2 id=\"%e5%85%b6%e4%bb%96%e6%95%b8%e6%93%9a%e5%ba%ab%e4%b8%ad%e7%9a%84dual%e8%a1%a8-xqbpDHxKEH\">\u5176\u4ed6\u6578\u64da\u5eab\u4e2d\u7684DUAL\u8868<\/h2>\n<p>\u96d6\u7136DUAL\u8868\u662fOracle\u6578\u64da\u5eab\u7684\u5c08\u6709\u7279\u6027\uff0c\u4f46\u5176\u4ed6\u6578\u64da\u5eab\u7cfb\u7d71\u4e5f\u6709\u985e\u4f3c\u7684\u6982\u5ff5\u3002\u4f8b\u5982\uff0c\u5728MySQL\u4e2d\uff0c\u96d6\u7136\u4e0d\u9700\u8981\u4f7f\u7528\u865b\u64ec\u8868\u4f86\u57f7\u884c\u7c21\u55ae\u67e5\u8a62\uff0c\u4f46\u53ef\u4ee5\u4f7f\u7528FROM DUAL\u4f86\u4fdd\u6301\u8207Oracle\u7684\u517c\u5bb9\u6027\u3002<\/p>\n<pre><code>SELECT NOW() FROM DUAL;\n<\/code><\/pre>\n<p>\u9019\u5728MySQL\u4e2d\u4e5f\u80fd\u6b63\u5e38\u57f7\u884c\uff0c\u8fd4\u56de\u7576\u524d\u7684\u65e5\u671f\u548c\u6642\u9593\u3002<\/p>\n<h2 id=\"%e7%b5%90%e8%ab%96-xqbpDHxKEH\">\u7d50\u8ad6<\/h2>\n<p>DUAL\u8868\u5728Oracle\u6578\u64da\u5eab\u4e2d\u662f\u4e00\u500b\u529f\u80fd\u5f37\u5927\u7684\u5de5\u5177\uff0c\u96d6\u7136\u5b83\u7684\u7d50\u69cb\u7c21\u55ae\uff0c\u4f46\u537b\u80fd\u5920\u652f\u6301\u591a\u7a2e\u67e5\u8a62\u64cd\u4f5c\u3002\u7121\u8ad6\u662f\u8a08\u7b97\u6578\u5b78\u8868\u9054\u5f0f\u3001\u7372\u53d6\u7cfb\u7d71\u6642\u9593\uff0c\u9084\u662f\u8abf\u7528\u5167\u5efa\u51fd\u6578\uff0cDUAL\u8868\u90fd\u80fd\u63d0\u4f9b\u4fbf\u6377\u7684\u89e3\u6c7a\u65b9\u6848\u3002\u4e86\u89e3DUAL\u8868\u7684\u4f7f\u7528\u65b9\u5f0f\uff0c\u5c0d\u65bc\u6578\u64da\u5eab\u958b\u767c\u8005\u4f86\u8aaa\u662f\u975e\u5e38\u91cd\u8981\u7684\uff0c\u56e0\u70ba\u5b83\u80fd\u5920\u63d0\u9ad8\u67e5\u8a62\u7684\u6548\u7387\u548c\u9748\u6d3b\u6027\u3002<\/p>\n<p>\u5982\u679c\u60a8\u5c0d\u65bc\u6578\u64da\u5eab\u7ba1\u7406\u6216\u5176\u4ed6\u76f8\u95dc\u6280\u8853\u6709\u8208\u8da3\uff0c\u6b61\u8fce\u8a2a\u554f\u6211\u5011\u7684\u7db2\u7ad9\u4e86\u89e3\u66f4\u591a\u8cc7\u8a0a\uff0c\u7279\u5225\u662f\u6211\u5011\u63d0\u4f9b\u7684<a href=\"https:\/\/server.hk\">\u9999\u6e2fVPS<\/a>\u548c<a href=\"https:\/\/server.hk\">\u96f2\u4f3a\u670d\u5668<\/a>\u89e3\u6c7a\u65b9\u6848\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"<p>\u63a2\u7d22\u6578\u64da\u5eab\u8868DUAL\u7684\u529f\u80fd\u8207\u7528\u9014\uff0c\u63ed\u793a\u5176\u5728\u67e5\u8a62\u4e2d\u7684\u91cd\u8981\u6027\u53ca\u80cc\u5f8c\u7684\u6280\u8853\u539f\u7406\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-163019","post","type-post","status-publish","format-standard","hentry","category-database"],"_links":{"self":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/163019","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=163019"}],"version-history":[{"count":1,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/163019\/revisions"}],"predecessor-version":[{"id":163020,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/163019\/revisions\/163020"}],"wp:attachment":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/media?parent=163019"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/categories?post=163019"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/tags?post=163019"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}