要检索只有两个特定值

Question

记录具有以下表中数据

Example Table 
ID Value 
1 a 
1 b 
1 c 
2 a 
2 b 
2 c 
3 a 
3 b 

我需要检索具有只有两个值a和b的ID记录。 所以我期待只有ID 3的记录。 谁能帮我查询

Answer 1

我想你可以做这样的事情

select 
ID, 
sum(case when value = 'a' then 1 
when value = 'b' then 1 
else 3 end) 

from 
table1 
group by id 
having 
sum (case when value = 'a' then 1 
when value = 'b' then 1 
else 3 end) =2 

SQL Fiddle

Answer 2

，将工作：

select x.id from 
(
    select id from mytable where value = 'a' 
    union all 
    select id from mytable where value = 'b' 
) x 
group by x.id 
having COUNT(*) = 2 
and not exists (select * from mytable t where t.id = x.id and value <> 'a' and value <> 'b')