select a.col1 from a
left join b on a.id=b.id
where b.date= '2007-1-1 '
select a.col1 from a
left join b on a.id=b.id
and b.date= '2007-1-1 '
如果没有区别,执行效率上那个更好啊
谢谢
------解决方案--------------------
Create Table A
(ID Int)
Create Table B
(ID Int,
Date Varchar(10))
GO
Insert A Select 1
Union All Select 2
Union All Select 3
Insert B Select 1, '2007-1-1 '
Union All Select 2, '2007-1-1 '
Union All Select 3, '2007-1-2 '
GO
select a.id from a
left join b on a.id=b.id
where b.date= '2007-1-1 '
select a.id from a
left join b on a.id=b.id
and b.date= '2007-1-1 '
GO
Drop Table A, B
--Result
/*
id
1
2
id
1
2
3
*/