declare @A表 table (c1 varchar(1),c2 varchar(8))
insert into @A表
select 'a',null union all
select 'b',null union all
select 'c',null union all
select 'd',null

declare @B表 table (id int,c1 varchar(10))
insert into @B表
select 1,'a' union all
select 2,'a,b,c' union all
select 3,'a,c'

update @A表
set c2=case when b.id is null then 'No' else 'Yes' end
from @A表 a left join @B表 b on charindex(','+a.c1+',',','+b.c1+',')>0

select * from @A表
/*
c1   c2
---- --------
a    Yes
b    Yes
c    Yes
d    No
*/

------解决方案--------------------

SQL code
USE CSDN
GO
declare @A表 table (c1 varchar(1),c2 varchar(8))
insert into @A表
select 'a',null union all
select 'b',null union all
select 'c',null union all
select 'd',null

declare @B表 table (id int,c1 varchar(10))
insert into @B表
select 1,'a' union all
select 2,'a,b,c' union all
select 3,'a,c'

UPDATE A
SET c2 = (CASE WHEN EXISTS(SELECT 1 FROM @B表 B WHERE CHARINDEX(','+A.c1+',', ','+B.c1+',') > 0) THEN 'YES' ELSE 'NO' END)
FROM @A表 A
WHERE c2 IS NULL

/*
c1    c2
a    YES
b    YES
c    YES
d    NO
*/