update a set flag=case when b.aid is not null then 'true' else 'false' end from a left join b on a.aid=b.aid
a表中没有flag字段。我只要一个select语句
select a.aid , flag=case when b.aid is not null then 'true' else 'false' end from a,b where a.aid=b.aid
select a.aid,flag=case when b.aid is null then 'false' else 'true' end from A表 a left join (select distinct aid from B表) b on a.aid=b.aid
a表中数据如 aid 1 2 3b表中 1 2 2我想得到输出aid flag 1 true 2 true 3 false
select a.aid , flag=case when b.aid is not null then 'true' else 'false' end from a left join b on a.aid=b.aid
select a.aid , flag=case when b.aid is not null then 'true' else 'false' end from a left join b on a.aid=b.aid group by a.aid, flag
--> By dobear_0922(小熊) 2008-10-10 15:08:58 --> 测试数据:@a declare @a table([aid] int) insert @a select 1 union all select 2 union all select 3 --> 测试数据:@b declare @b table([aid] int) insert @b select 1 union all select 2 union all select 2select aid,flag=isnull((select top 1 'true' from @b where aid=a.aid), 'false') from @a a /* aid flag ----------- ---- 1 true 2 true 3 fals */
select aid,flag=isnull((select top 1 cast('true' as varchar(8)) from b where aid=a.aid), 'false') from a /* aid flag ----------- -------- 1 true 2 true 3 false */
update a
set flag=case when b.aid is not null then 'true' else 'false' end
from
a
left join
b on a.aid=b.aid
flag=case when b.aid is not null then 'true' else 'false' end from a,b
where
a.aid=b.aid
select a.aid,flag=case when b.aid is null then 'false' else 'true' end
from A表 a
left join (select distinct aid from B表) b
on a.aid=b.aid
aid
1
2
3b表中
1
2
2我想得到输出aid flag
1 true
2 true
3 false
flag=case when b.aid is not null then 'true' else 'false' end
from a left join b on a.aid=b.aid
flag=case when b.aid is not null then 'true' else 'false' end
from a left join b on a.aid=b.aid
group by a.aid, flag
--> 测试数据:@a
declare @a table([aid] int)
insert @a
select 1 union all
select 2 union all
select 3
--> 测试数据:@b
declare @b table([aid] int)
insert @b
select 1 union all
select 2 union all
select 2select aid,flag=isnull((select top 1 'true' from @b where aid=a.aid), 'false')
from @a a /*
aid flag
----------- ----
1 true
2 true
3 fals
*/
from a /*
aid flag
----------- --------
1 true
2 true
3 false
*/