问题描述
|
我的目标是执行两个不同的查询,然后将它们组合。
我的代码是:
SELECT * FROM some tables WHERE ... ORDER BY field1 LIMIT 0,1
UNION
SELECT * FROM some tables WHERE ...
我收到以下错误:
#1221-UNION和ORDER BY的使用不正确
重要的是ORDER BY仅用于第一个查询。如何执行此任务?
解决方法
您可以使用括号允许对单个查询使用
ORDER
/LIMIT
:
(SELECT * FROM some tables WHERE ... ORDER BY field1 LIMIT 0,1)
UNION
(SELECT * FROM some tables WHERE ...)
ORDER BY 1 /* optional -- applies to the UNIONed result */
LIMIT 0,100 /* optional -- applies to the UNIONed result */
, SELECT * FROM (SELECT * FROM some tables WHERE ... ORDER BY field1 LIMIT 0,1) x
UNION ALL
SELECT * FROM some tables WHERE ...
注意the5的用法:
“ 6”从结果集中删除重复的行,并且数据库在执行此操作之前将所有行排序(因此对整个结果集进行了排序)
UNION ALL
保留顺序和重复项
, 只需将所有内容放在圆括号中即可:
(SELECT * FROM table1 ORDER BY datetime )
UNION
(SELECT * FROM table2 ORDER BY datetime DESC)
, (SELECT user_id AS id FROM tbl_user)
UNION
(SELECT address_id AS id FROM tbl_address)
ORDER BY id ASC LIMIT 10