{"id":43,"date":"2020-12-28T19:12:51","date_gmt":"2020-12-28T11:12:51","guid":{"rendered":"https:\/\/www.52dixiaowo.com\/database\/?p=43"},"modified":"2020-12-28T19:12:52","modified_gmt":"2020-12-28T11:12:52","slug":"dql-%e6%95%b0%e6%8d%ae%e7%9a%84%e6%9f%a5%e8%af%a2","status":"publish","type":"post","link":"https:\/\/www.52dixiaowo.com\/db\/post-43.html","title":{"rendered":"DQL — \u6570\u636e\u7684\u67e5\u8be2"},"content":{"rendered":"\n
1.\u67e5\u8be2\u8bed\u6cd5\uff1a\uff08\u8fd9\u4e2a\u8bed\u6cd5\u4e0d\u5305\u542b\u5173\u952e\u5b57\uff0c\u51fd\u6570\uff09<\/h5>\n\n\n\n
select\n    \u5b57\u6bb5\u5217\u8868\nfrom\n    \u8868\u540d\u5217\u8868\nwhere\n    \u6761\u4ef6\u5217\u8868\ngroup by\n    \u5206\u7ec4\u5b57\u6bb5\nhaving\n    \u5206\u7ec4\u4e4b\u540e\u7684\u6761\u4ef6\norder by\n    \u6392\u5e8f\nlimit\n    \u5206\u9875\u9650\u5b9a<\/code><\/pre>\n\n\n\n
2.\u7b80\u5355\u67e5\u8be2\u4e3e\u4f8b<\/h5>\n\n\n\n
\u67e5\u8be2\u8868\u4e2d\u6240\u6709\u7684\u6570\u636e<\/p>\n\n\n\n
select * form \u8868\u540d;<\/code><\/pre>\n\n\n\n
\u67e5\u8be2\u591a\u5217\u5b57\u6bb5<\/p>\n\n\n\n
select \n        \u52171,       -- \u6ce8\u91ca1\n        \u52172...     -- \u6ce8\u91ca2\nfrom \n        \u8868\u540d;<\/code><\/pre>\n\n\n\n
\u67e5\u8be2\u7ed3\u679c\u53bb\u91cd\u590d\uff1a<\/p>\n\n\n\n
select distinct \u5217\u540d\u79f0 from \u8868\u540d\u79f0;<\/code><\/pre>\n\n\n\n
\u7ed3\u7b97 \u591a \u5217\u7684\u548c\u5c55\u793a\u7ed3\u679c\uff08\u8fd9\u91cc\u6709 2 \u5217\uff0c\u4e14\u5047\u8bbe\u628a\u52172 \u4e3a Null  \u66ff\u6362\u4e3a 0\uff09<\/p>\n\n\n\n
select \u52171,\u52172, \u52171+IFNULL(\u52172,0) from \u8868\u540d;<\/code><\/pre>\n\n\n\n
\u7ed9\u67e5\u8be2\u7ed3\u679c\u5217\u8d77\u522b\u540d\uff08 as \u53ef\u4ee5\u7701\u7565\uff09<\/p>\n\n\n\n
select \u539f\u5217\u540d as \u5c55\u793a\u5217\u540d from \u8868\u540d\u79f0;<\/code><\/pre>\n\n\n\n
\u67e5\u8be2\u6307\u5b9a\u6761\u4ef6\u7684\u4e00\u6761\u6570\u636e \uff08\u5047\u5982\u67e5\u8be2\u67d0\u4e2a\u5217\u5305\u542b\u67d0\u4e2a\u503c\uff09<\/p>\n\n\n\n
select * from \u8868\u540d where \u5217 = \u503c;<\/code><\/pre>\n\n\n\n
\u67e5\u8be2\u6ee1\u8db3\u591a\u6761\u4ef6\u6570\u636e\uff1a\uff08\u8fd9\u91cc\u662f\u5305\u542b\u591a\u4e2a\u5b57\u6bb5\uff09<\/p>\n\n\n\n
select * from \u8868\u540d where \u52171=\u503c1 and \u52172=\u503c2;<\/code><\/pre>\n\n\n\n
\u67e5\u8be2\u6ee1\u8db3\u67d0\u4e00\u6761\u4ef6\u6570\u636e\uff1a\uff08\u8fd9\u91cc\u662f\u5305\u542b\u5176\u4e2d\u4e00\u4e2a\u5b57\u6bb5\uff09<\/p>\n\n\n\n
select * from \u8868\u540d where \u52171=\u503c1 or \u52172=\u503c2;<\/code><\/pre>\n\n\n\n
\u67e5\u8be2\u7ed3\u679c\u5347\u5e8f\u6392\u5217\uff1a<\/p>\n\n\n\n
select * from \u8868\u540d order by \u52171\uff0c\u52172...\uff1b(\u9ed8\u8ba4asc)<\/code><\/pre>\n\n\n\n
\u67e5\u8be2\u7ed3\u679c\u964d\u5e8f\uff1a<\/p>\n\n\n\n
select * from \u8868\u540d order by \u52171 desc, \u52172desc...;<\/code><\/pre>\n\n\n\n
\u5206\u7ec4\u67e5\u8be2\uff08\u52a0\u5982\u5206\u7ec4\u5b57\u6bb5 sex\uff0c\u5c55\u793a\u5b57\u6bb51 AVG(math)\uff0c\u5c55\u793a\u5b57\u6bb52 COUNT(id) )<\/p>\n\n\n\n
(\u5206\u7ec4\u4e4b\u540e\u4e0d\u8981\u5199\u65e0\u5173\u5b57\u6bb5\uff0c\u5c55\u793a\u5b57\u6bb5\u4e00\u822c\u4e3a\u805a\u5408\u51fd\u6570\uff09<\/p>\n\n\n\n
select \u5206\u7ec4\u5b57\u6bb5,\u5c55\u793a\u5b57\u6bb51,\u5c55\u793a\u5b57\u6bb52... from \u8868\u540d group by \u5206\u7ec4\u5b57\u6bb5;<\/code><\/pre>\n\n\n\n
\u5206\u7ec4\u9650\u5b9a\uff08\u5982\u679c\u5206\u7ec4\u540e\uff0chaving \u6761\u4ef6\u5982\u679c\u4e0d\u7b26\u5408\uff0c\u5c31\u4e0d\u663e\u793a\u6b64\u5b57\u6bb5\uff09<\/p>\n\n\n\n
(\u8fd9\u91cc\uff0c\u5047\u8bbe\u5206\u7ec4\u540e\uff0c\u5176\u4e2d\u4e00\u7ec4\u7684\u5305\u542b id \u4e0d\u4e3aNull \u7684\u8bb0\u5f55\u6570\u4e0d\u5c11\u4e8e 2\uff0c\u624d\u663e\u793a\uff09<\/p>\n\n\n\n
( group by \u548c having \uff0c\u5747\u53ef\u4ee5\u4f7f\u7528\u524d\u9762\u8d77\u7684\u81ea\u5b9a\u4e49\u7684 \u5217\u522b\u540d\uff09<\/p>\n\n\n\n
select \u5206\u7ec4\u5b57\u6bb5,\u5c55\u793a\u5b57\u6bb5 from group by \u5206\u7ec4\u5b57\u6bb5 having count(id)>2;<\/code><\/pre>\n\n\n\n
3.\u6761\u4ef6\u67e5\u8be2<\/h5>\n\n\n\n
where \u5b50\u53e5\u540e\u8ddf\u6761\u4ef6<\/p>\n\n\n\n
\u5e38\u7528\u8fd0\u7b97<\/p>\n\n\n\n
><\/td>\u5927\u4e8e<\/td><\/tr>
<<\/td>\u5c0f\u4e8e<\/td><\/tr>
<=<\/td>\u5c0f\u4e8e\u7b49\u4e8e<\/td><\/tr>
>=<\/td>\u5927\u4e8e\u7b49\u4e8e<\/td><\/tr>
=<\/td>\u7b49\u4e8e<\/td><\/tr>
<>  \u6216  !=<\/td>\u4e0d\u7b49\u4e8e<\/td><\/tr>
between … and<\/td>\u5728 … \u4e4b\u95f4<\/td><\/tr>
in(\u96c6\u5408)<\/td>\u5728 … \u4e4b\u4e2d<\/td><\/tr>
is null<\/td>\u662f null<\/td><\/tr>
is not null<\/td>\u4e0d\u662f  null<\/td><\/tr>
and \u6216 &&<\/td>\u4e14<\/td><\/tr>
or \u6216 ||<\/td>\u6216<\/td><\/tr>
not \u6216 \uff01<\/td>\u975e<\/td><\/tr>
like<\/td>\u6a21\u7cca\u8fd0\u7b97<\/td><\/tr>
_<\/td>\u5355\u4e2a\u5b57\u7b26<\/td><\/tr>
%<\/td>\u591a\u4e2a\u4efb\u610f\u5b57\u7b26<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
\u67e5\u8be2\u59d3\u9a6c\u7684\u4eba\uff0c<\/p>\n\n\n\n
select * from \u8868\u540d where name like '\u9a6c';<\/code><\/pre>\n\n\n\n
\u67e5\u8be2\u7b2c\u4e8c\u4e2a\u5b57\u662f \u2019\u5316\u2018 \u7684\u4eba<\/p>\n\n\n\n
select * from \u8868\u540d where name like '_\u5316%';<\/code><\/pre>\n\n\n\n
\u67e5\u8be2\u59d3\u540d\u662f\u4e09\u4e2a\u5b57\u7684\u4eba\uff08\u4e09\u4e2a\u77ed\u6760 _ \uff09<\/p>\n\n\n\n
select * from \u8868\u540d where name like '___';<\/code><\/pre>\n\n\n\n
\u67e5\u8be2\u59d3\u540d\u4e2d\u5305\u542b \u2018\u9a6c\u2019 \u5b57\u7684\u4eba<\/p>\n\n\n\n
select * from \u8868\u540d where name like '%\u9a6c%';<\/code><\/pre>\n\n\n\n
4.\u805a\u5408\u51fd\u6570<\/h5>\n\n\n\n
\u805a\u5408\u51fd\u6570\u662f\u5c06\u67d0\u4e00\u5217\u4f5c\u4e3a\u4e00\u4e2a\u6574\u4f53\uff0c\u7136\u540e\u8fdb\u884c\u8ba1\u7b97<\/p>\n\n\n\n
\uff08\u805a\u5408\u51fd\u6570\u9ed8\u8ba4\u4f1a\u6392\u9664 null \uff0c\u53ef\u8ba1\u7b97\u4e3b\u952e\uff0c\u6216\u914d\u5408 ifnull \u51fd\u6570\uff09<\/p>\n\n\n\n
\u8ba1\u7b97\u67d0\u4e2a\u5217\u8bb0\u5f55\u6761\u6570\uff08\u5982\u679c\u662f * ,\u4f1a\u4f7f\u7528\u6570\u636e\u6700\u591a\u7684\u5217\uff0c\u8ba1\u7b97\u51fa\u6240\u6709\u8bb0\u5f55\u7684\u6761\u6570\uff09<\/p>\n\n\n\n
select count(\u5217\u540d) from \u8868\u540d;<\/code><\/pre>\n\n\n\n
\u8ba1\u7b97\u67d0\u4e2a\u5217\u6700\u5927\u7684\u8bb0\u5f55<\/p>\n\n\n\n
select MAX(\u5217\u540d) from \u8868\u540d;<\/code><\/pre>\n\n\n\n
\u8ba1\u7b97\u67d0\u4e2a\u5217\u6700\u5c0f\u7684\u8bb0\u5f55<\/p>\n\n\n\n
select MIN(\u5217\u540d) from \u8868\u540d;<\/code><\/pre>\n\n\n\n
\u8ba1\u7b97\u5217\u7684\u548c<\/p>\n\n\n\n
select SUM(\u5217\u540d) from \u8868\u540d;<\/code><\/pre>\n\n\n\n
\u8ba1\u7b97\u5217\u7684\u5e73\u5747\u503c<\/p>\n\n\n\n
select AVG(\u5217\u540d) from \u8868\u540d;<\/code><\/pre>\n\n\n\n
5.\u5206\u9875\u67e5\u8be2\uff08\u4e0d\u540c\u7684\u6570\u636e\u5e93\uff0c\u5b9e\u73b0\u7684\u65b9\u5f0f\u4e0d\u4e00\u6837\uff0c\u8fd9\u91cc\u4ec5\u9650\u4e8e mysql\uff09<\/h5>\n\n\n\n
\u8bed\u6cd5\uff1alimit \u5f00\u59cb\u7d22\u5f15\uff0c\u6bcf\u9875\u663e\u793a\u6761\u6570<\/p>\n\n\n\n
\uff08\u516c\u5f0f\uff1a\u5f00\u59cb\u7684\u7d22\u5f15 = (\u5f53\u524d\u9875\u7801 -1) * \u6bcf\u9875\u663e\u793a\u7684\u6761\u6570 <\/p>\n\n\n\n
\u67e5\u8be2\u5b66\u751f\u6570\u636e\u8868\uff0c\u4e00\u6b21\u663e\u793a3\u6761\uff0c\u7b2c\u4e00\u9875<\/p>\n\n\n\n
select * from student limit 0,3;<\/code><\/pre>\n\n\n\n
\u67e5\u8be2\u5b66\u751f\u6570\u636e\u8868\uff0c\u4e00\u6b21\u663e\u793a3\u6761\uff0c\u7b2c2\u9875<\/p>\n\n\n\n
select * from student limit 3,3;<\/code><\/pre>\n\n\n\n
\u67e5\u8be2\u5b66\u751f\u6570\u636e\u8868\uff0c\u4e00\u6b21\u663e\u793a3\u6761\uff0c\u7b2c3\u9875<\/p>\n\n\n\n
select * from student limit 6,3;<\/code><\/pre>\n\n\n\n
<\/p>\n","protected":false},"excerpt":{"rendered":"
1.\u67e5\u8be2\u8bed\u6cd5\uff1a\uff08\u8fd9\u4e2a\u8bed\u6cd5\u4e0d\u5305\u542b\u5173\u952e\u5b57\uff0c\u51fd\u6570\uff09 2.\u7b80\u5355\u67e5\u8be2\u4e3e\u4f8b \u67e5\u8be2\u8868\u4e2d\u6240\u6709\u7684\u6570\u636e \u67e5\u8be2\u591a\u5217\u5b57\u6bb5 \u67e5\u8be2\u7ed3\u679c\u53bb\u91cd… \u7ee7\u7eed\u9605\u8bfb DQL — \u6570\u636e\u7684\u67e5\u8be2<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[4],"tags":[],"_links":{"self":[{"href":"https:\/\/www.52dixiaowo.com\/db\/wp-json\/wp\/v2\/posts\/43"}],"collection":[{"href":"https:\/\/www.52dixiaowo.com\/db\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.52dixiaowo.com\/db\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.52dixiaowo.com\/db\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.52dixiaowo.com\/db\/wp-json\/wp\/v2\/comments?post=43"}],"version-history":[{"count":1,"href":"https:\/\/www.52dixiaowo.com\/db\/wp-json\/wp\/v2\/posts\/43\/revisions"}],"predecessor-version":[{"id":44,"href":"https:\/\/www.52dixiaowo.com\/db\/wp-json\/wp\/v2\/posts\/43\/revisions\/44"}],"wp:attachment":[{"href":"https:\/\/www.52dixiaowo.com\/db\/wp-json\/wp\/v2\/media?parent=43"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.52dixiaowo.com\/db\/wp-json\/wp\/v2\/categories?post=43"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.52dixiaowo.com\/db\/wp-json\/wp\/v2\/tags?post=43"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}