获取基于特定值的记录（如果存在值）。如果值不存在，则根据其他值获取记录

Question

我有下表：

A  |  B  | C
1    I    as 
2    E    as
1    E    sa
3    I    as 
2    I    sa
3    I    sa 
4    E    as 
4    E    ad
1    I    as
2    D    sd
3    D    sa

OUTPUT表：

A  |  B  | C 
1    I    as
2    E    as
1    E    sa 
3    I    as
3    I    sa  
4    E    as 
4    E    ad

应选择所有那些在字段B中具有值E的记录。如果字段B中记录I的相同记录（对于字段A和C），则不应选择它。如果A和B中的值没有值E，则应选择包含字段I的记录。

Answer 1

我想我知道你在问什么：

select A, B, C
from myTable t1
where B='E'
or (B='I' and not exists (
  select * 
  from myTable t2
  where t2.A=t1.A
  and t2.C=t1.C
  and t2.B='E'
))