sql - sql查询简化，负担更轻

Question

我需要通过使用连接或任何其他方式尽可能简化以下查询......

select polid
  from polver
  where idmkey = 'idm3'
    and polid in ( select polid
                     from polver
                     where idmkey = 'idm2'
                       and polid in ( select polid
                                        from polver
                                        where idmkey='idm1' ) );

Answer 1

您可以通过以下方式使用组：

select  polid
from    polver
group by
        polid
having  max(case when idmkey = 'idm1' then 1 end) = 1
        and max(case when idmkey = 'idm2' then 1 end) = 1
        and max(case when idmkey = 'idm3' then 1 end) = 1

Answer 2

select polid from polver
where idmkey in ('idm1', 'idm2', 'idm3') 
group by polid
having count(distinct idmkey) = 3