<\/span><\/h3>\n\n\n\ngbase> select ifnull(null,0) from dual;\r\n+----------------+\r\n| ifnull(null,0) |\r\n+----------------+\r\n| 0 |\r\n+----------------+\r\n1 row in set (Elapsed: 00:00:00.00)\r\n<\/code><\/pre>\n\n\n\n<\/span>\u5b57\u7b26<\/span><\/h3>\n\n\n\ngbase> select ifnull(null,'abcd') from dual;\r\n+---------------------+\r\n| ifnull(null,'abcd') |\r\n+---------------------+\r\n| abcd |\r\n+---------------------+\r\n1 row in set (Elapsed: 00:00:00.00)\r\n<\/code><\/pre>\n\n\n\n<\/span>Date<\/span><\/h3>\n\n\n\ngbase> select ifnull(null,now()) from dual;\r\n+---------------------+\r\n| ifnull(null,now()) |\r\n+---------------------+\r\n| 2020-12-22 09:22:09 |\r\n+---------------------+\r\n1 row in set (Elapsed: 00:00:00.01)\r\n<\/code><\/pre>\n\n\n\n<\/span>nvl(expr1,expr2)<\/span><\/h2>\n\n\n\n\u4e0eifnull\u5b8c\u5168\u76f8\u540c\u3002\u5982\u679cexpr1\u4e3anull,\u5219\u8fd4\u56deexpr2,\u5426\u5219\u8fd4\u56deexpr1\u81ea\u5df1\u3002<\/p>\n\n\n\n
gbase> select nvl(null,1) from dual;\r\n+-------------+\r\n| nvl(null,1) |\r\n+-------------+\r\n| 1 |\r\n+-------------+\r\n1 row in set (Elapsed: 00:00:00.01)\r\n\r\ngbase> select nvl(null,'abcd') from dual;\r\n+------------------+\r\n| nvl(null,'abcd') |\r\n+------------------+\r\n| abcd |\r\n+------------------+\r\n1 row in set (Elapsed: 00:00:00.01)\r\n\r\ngbase> select nvl(null,now()) from dual;\r\n+---------------------+\r\n| nvl(null,now()) |\r\n+---------------------+\r\n| 2020-12-22 09:26:08 |\r\n+---------------------+\r\n1 row in set (Elapsed: 00:00:00.00)\r\n<\/code><\/pre>\n\n\n\n<\/span>nullif(expr1,expr2)<\/span><\/h2>\n\n\n\n\u5982\u679c expr1 = expr2 \u6210\u7acb\uff0c\u8fd4\u56de\u503c\u4e3a NULL\uff0c\u5426\u5219\u8fd4\u56de\u503c\u4e3a expr1\u3002
\u7b49\u4ef7\u4e8e CASE WHEN expr1 = expr2 THEN NULL ELSE expr1 END\u3002<\/p>\n\n\n\n
\u6ce8\u610f\u5185\u90e8\u7684\u6570\u636e\u7c7b\u578b\u5982\u679c\u4e0d\u540c\uff0c\u4f1a\u81ea\u52a8\u8f6c\u6362\u540e\u518d\u6bd4\u8f83\u3002\u6240\u4ee5\u6570\u5b571\u548c\u5b57\u7b26\u4e321\u4e5f\u662f\u76f8\u7b49\u7684\u3002<\/p>\n\n\n\n
gbase> select nullif(1,1) from dual;\r\n+-------------+\r\n| nullif(1,1) |\r\n+-------------+\r\n| NULL |\r\n+-------------+\r\n1 row in set (Elapsed: 00:00:00.01)\r\n\r\ngbase> select nullif(1,'1') from dual;\r\n+---------------+\r\n| nullif(1,'1') |\r\n+---------------+\r\n| NULL |\r\n+---------------+\r\n1 row in set (Elapsed: 00:00:00.01)\r\n\r\ngbase> select nullif('1',1) from dual;\r\n+---------------+\r\n| nullif('1',1) |\r\n+---------------+\r\n| NULL |\r\n+---------------+\r\n1 row in set (Elapsed: 00:00:00.01)\r\n\r\ngbase> select nullif('1',2) from dual;\r\n+---------------+\r\n| nullif('1',2) |\r\n+---------------+\r\n| 1 |\r\n+---------------+\r\n1 row in set (Elapsed: 00:00:00.01)\r\n\r\ngbase>\r\n<\/code><\/pre>","protected":false},"excerpt":{"rendered":"\u5357\u5927\u901a\u7528GBase 8a\u5185\u7f6e\u51e0\u4e2a\u51fd\u6570\u5b9e\u73b0\u5bf9null\u503c\u7684\u5904\u7406\uff0c\u4e3b\u8981\u662f\u4e3a\u4e86\u907f\u514dnull\u503c\u53c2\u4e0e\u8fd0\u7b97\u5bfc\u81f4\u7ed3\u679c\u548c\u9884\u671f\u4e0d\u7b26\u3002<\/p>","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[3],"tags":[36],"class_list":["post-2529","post","type-post","status-publish","format-standard","hentry","category-gbase8a","tag-36"],"_links":{"self":[{"href":"https:\/\/www.gbase8.cn\/en\/wp-json\/wp\/v2\/posts\/2529","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.gbase8.cn\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.gbase8.cn\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.gbase8.cn\/en\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.gbase8.cn\/en\/wp-json\/wp\/v2\/comments?post=2529"}],"version-history":[{"count":1,"href":"https:\/\/www.gbase8.cn\/en\/wp-json\/wp\/v2\/posts\/2529\/revisions"}],"predecessor-version":[{"id":2530,"href":"https:\/\/www.gbase8.cn\/en\/wp-json\/wp\/v2\/posts\/2529\/revisions\/2530"}],"wp:attachment":[{"href":"https:\/\/www.gbase8.cn\/en\/wp-json\/wp\/v2\/media?parent=2529"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.gbase8.cn\/en\/wp-json\/wp\/v2\/categories?post=2529"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.gbase8.cn\/en\/wp-json\/wp\/v2\/tags?post=2529"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}