\u5728\u7576\u4eca\u7684\u6578\u64da\u5eab\u7ba1\u7406\u4e2d\uff0c\u8868\u7684\u8a2d\u8a08\u548c\u7d50\u69cb\u5c0d\u65bc\u6578\u64da\u7684\u5b58\u5132\u548c\u6aa2\u7d22\u81f3\u95dc\u91cd\u8981\u3002DUAL\u8868\u662fOracle\u6578\u64da\u5eab\u4e2d\u7684\u4e00\u500b\u7279\u6b8a\u8868\uff0c\u8a31\u591a\u958b\u767c\u8005\u548c\u6578\u64da\u5eab\u7ba1\u7406\u54e1\u5728\u4f7f\u7528SQL\u67e5\u8a62\u6642\u7d93\u5e38\u6703\u9047\u5230\u5b83\u3002\u90a3\u9ebc\uff0cDUAL\u8868\u7a76\u7adf\u662f\u4ec0\u9ebc\uff1f\u5b83\u7684\u5b58\u5728\u662f\u5426\u771f\u5be6\uff1f\u672c\u6587\u5c07\u6df1\u5165\u63a2\u8a0eDUAL\u8868\u7684\u7279\u6027\u53ca\u5176\u5728\u6578\u64da\u5eab\u4e2d\u7684\u4f5c\u7528\u3002<\/p>\n
DUAL\u8868\u662f\u4e00\u500b\u865b\u64ec\u8868\uff0c\u5b58\u5728\u65bcOracle\u6578\u64da\u5eab\u4e2d\u3002\u5b83\u7684\u4e3b\u8981\u7528\u9014\u662f\u63d0\u4f9b\u4e00\u500b\u7c21\u55ae\u7684\u65b9\u5f0f\u4f86\u57f7\u884c\u67e5\u8a62\uff0c\u7279\u5225\u662f\u5728\u4e0d\u9700\u8981\u5f9e\u4efb\u4f55\u5be6\u969b\u8868\u4e2d\u6aa2\u7d22\u6578\u64da\u6642\u3002DUAL\u8868\u7684\u7d50\u69cb\u975e\u5e38\u7c21\u55ae\uff0c\u901a\u5e38\u53ea\u6709\u4e00\u884c\u548c\u4e00\u5217\uff0c\u9019\u4e00\u5217\u7684\u540d\u7a31\u70ba”DUMMY”\uff0c\u5176\u503c\u70ba’X’\u3002<\/p>\n
DUAL\u8868\u6700\u521d\u662f\u70ba\u4e86\u652f\u6301\u67d0\u4e9bSQL\u67e5\u8a62\u800c\u8a2d\u8a08\u7684\u3002\u96a8\u8457\u6642\u9593\u7684\u63a8\u79fb\uff0c\u9019\u500b\u8868\u7684\u4f7f\u7528\u9010\u6f38\u666e\u53ca\uff0c\u6210\u70ba\u4e86Oracle\u6578\u64da\u5eab\u4e2d\u4e00\u500b\u4e0d\u53ef\u6216\u7f3a\u7684\u7d44\u6210\u90e8\u5206\u3002\u96d6\u7136\u5728\u5176\u4ed6\u6578\u64da\u5eab\u7cfb\u7d71\u4e2d\u4e26\u4e0d\u5b58\u5728DUAL\u8868\uff0c\u4f46\u5176\u529f\u80fd\u53ef\u4ee5\u901a\u904e\u5176\u4ed6\u65b9\u5f0f\u5be6\u73fe\u3002<\/p>\n
DUAL\u8868\u7684\u4e3b\u8981\u7528\u9014\u5305\u62ec\uff1a<\/p>\n
SELECT SYSDATE FROM DUAL;<\/code><\/pre>\n\u9019\u689d\u67e5\u8a62\u5c07\u8fd4\u56de\u7576\u524d\u7684\u7cfb\u7d71\u65e5\u671f\u548c\u6642\u9593\u3002<\/p>\n
\n- \u6e2c\u8a66\u67e5\u8a62\uff1a<\/strong>\u958b\u767c\u8005\u5728\u6e2c\u8a66SQL\u67e5\u8a62\u6642\uff0c\u5e38\u5e38\u4f7f\u7528DUAL\u8868\u4f86\u9a57\u8b49\u8a9e\u6cd5\u7684\u6b63\u78ba\u6027\u3002<\/li>\n
- \u8fd4\u56de\u5e38\u91cf\u503c\uff1a<\/strong>\u5982\u679c\u9700\u8981\u8fd4\u56de\u4e00\u500b\u5e38\u91cf\u503c\uff0c\u4e5f\u53ef\u4ee5\u4f7f\u7528DUAL\u8868\u3002\u4f8b\u5982\uff1a<\/li>\n<\/ul>\n
SELECT 'Hello, World!' FROM DUAL;<\/code><\/pre>\n\u9019\u689d\u67e5\u8a62\u5c07\u8fd4\u56de\u5b57\u7b26\u4e32”Hello, World!”\u3002<\/p>\n
DUAL\u8868\u7684\u7279\u6027<\/h2>\n
DUAL\u8868\u6709\u4ee5\u4e0b\u5e7e\u500b\u7279\u6027\uff1a<\/p>\n
\n- \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\u7d50\u69cb\u3002<\/li>\n
- \u55ae\u884c\u55ae\u5217\uff1a<\/strong>DUAL\u8868\u53ea\u6709\u4e00\u884c\u548c\u4e00\u5217\uff0c\u9019\u4f7f\u5f97\u5b83\u5728\u57f7\u884c\u7c21\u55ae\u67e5\u8a62\u6642\u975e\u5e38\u9ad8\u6548\u3002<\/li>\n
- \u517c\u5bb9\u6027\uff1a<\/strong>\u96d6\u7136DUAL\u8868\u662fOracle\u7279\u6709\u7684\uff0c\u4f46\u5176\u4ed6\u6578\u64da\u5eab\u7cfb\u7d71\u4e5f\u53ef\u4ee5\u901a\u904e\u985e\u4f3c\u7684\u65b9\u5f0f\u4f86\u5be6\u73fe\u76f8\u540c\u7684\u529f\u80fd\u3002<\/li>\n<\/ul>\n
\u5176\u4ed6\u6578\u64da\u5eab\u7cfb\u7d71\u4e2d\u7684\u985e\u4f3c\u6982\u5ff5<\/h2>\n
\u5728\u5176\u4ed6\u6578\u64da\u5eab\u7cfb\u7d71\u4e2d\uff0c\u96d6\u7136\u6c92\u6709\u540d\u70baDUAL\u7684\u8868\uff0c\u4f46\u53ef\u4ee5\u4f7f\u7528\u5176\u4ed6\u65b9\u6cd5\u4f86\u9054\u5230\u76f8\u4f3c\u7684\u6548\u679c\u3002\u4f8b\u5982\uff0c\u5728MySQL\u4e2d\uff0c\u53ef\u4ee5\u76f4\u63a5\u4f7f\u7528SELECT\u8a9e\u53e5\u800c\u4e0d\u9700\u8981\u6307\u5b9a\u8868\u540d\uff1a<\/p>\n
SELECT NOW();<\/code><\/pre>\n\u9019\u689d\u67e5\u8a62\u5c07\u8fd4\u56de\u7576\u524d\u7684\u65e5\u671f\u548c\u6642\u9593\uff0c\u800c\u4e0d\u9700\u8981\u4f9d\u8cf4\u65bc\u4efb\u4f55\u7279\u5b9a\u7684\u8868\u3002<\/p>\n
\u7d50\u8ad6<\/h2>\n
DUAL\u8868\u5728Oracle\u6578\u64da\u5eab\u4e2d\u662f\u4e00\u500b\u975e\u5e38\u91cd\u8981\u7684\u7d44\u4ef6\uff0c\u96d6\u7136\u5b83\u7684\u5b58\u5728\u662f\u865b\u64ec\u7684\uff0c\u4f46\u5b83\u5728\u57f7\u884c\u67e5\u8a62\u6642\u63d0\u4f9b\u4e86\u6975\u5927\u7684\u4fbf\u5229\u3002\u7121\u8ad6\u662f\u9032\u884c\u8a08\u7b97\u3001\u6e2c\u8a66\u67e5\u8a62\u9084\u662f\u8fd4\u56de\u5e38\u91cf\u503c\uff0cDUAL\u8868\u90fd\u80fd\u5920\u9ad8\u6548\u5730\u5b8c\u6210\u4efb\u52d9\u3002\u5c0d\u65bc\u958b\u767c\u8005\u4f86\u8aaa\uff0c\u7406\u89e3DUAL\u8868\u7684\u7279\u6027\u548c\u7528\u9014\u662f\u975e\u5e38\u91cd\u8981\u7684\uff0c\u9019\u5c07\u6709\u52a9\u65bc\u63d0\u9ad8\u4ed6\u5011\u5728\u6578\u64da\u5eab\u64cd\u4f5c\u4e2d\u7684\u6548\u7387\u3002<\/p>\n
\u5982\u679c\u60a8\u5c0d\u65bc\u6578\u64da\u5eab\u7ba1\u7406\u6216\u5176\u4ed6\u6280\u8853\u554f\u984c\u6709\u8208\u8da3\uff0c\u6b61\u8fce\u8a2a\u554f\u6211\u5011\u7684\u7db2\u7ad9\u4e86\u89e3\u66f4\u591a\u8cc7\u8a0a\uff0c\u7279\u5225\u662f\u6709\u95dc\u9999\u6e2fVPS<\/a>\u548c\u96f2\u4f3a\u670d\u5668<\/a>\u7684\u89e3\u6c7a\u65b9\u6848\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"\u63a2\u7d22DUAL\u662f\u771f\u5be6\u7684\u8868\u55ce\uff1f\u4e86\u89e3\u5176\u8a2d\u8a08\u3001\u529f\u80fd\u53ca\u771f\u5be6\u6027\uff0c\u63ed\u958b\u9019\u6b3e\u624b\u9336\u7684\u795e\u79d8\u9762\u7d17\u3002<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[101],"tags":[],"class_list":["post-61229","post","type-post","status-publish","format-standard","hentry","category-database"],"_links":{"self":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/61229","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"}],"author":[{"embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/comments?post=61229"}],"version-history":[{"count":1,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/61229\/revisions"}],"predecessor-version":[{"id":61230,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/61229\/revisions\/61230"}],"wp:attachment":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/media?parent=61229"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/categories?post=61229"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/tags?post=61229"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}