为什么这样我就取不到数据？应当怎样修改？

Question

表register为用户注册信息表，里面有个datetime类型的字段TIME用于记录注册时间，现在想查询最早和最晚注册的用户信息。我写的sql语句：select * from register where TIME IN (select max(TIME),min(TIME) from register)

Answer 1

不明白你的需求,如果是取两个时间点之间的所有数据:
select * from register where TIME Between (select max(TIME) from register) and (select min(TIME) from register)

Answer 2

这种情况，最好是UNION ALL：
SELECT * FROM [register] WHERE [time] = (select max([TIME]) from [register])
UNION ALL
SELECT * FROM [register] WHERE [time] = (select min([TIME]) from [register])
还要注意给time字段建个索引。

Answer 3

SQL语句要讲求效率。UNION的方式效率更高
SELECT * FROM [register] WHERE [time] = (select max([TIME]) from [register])
UNION
SELECT * FROM [register] WHERE [time] = (select min([TIME]) from [register])