Re: GROUP BY question

If you have an index on the email column, the following SQL will be very efficient.

select a.email, a.name, a.id
from table a
where exists (
  select null
  from table b
  where b.email = a.email
  and b.id != a.id);

--

William WW LEE.
E-Mail: william_at_alumni.cuhk.edu.hk
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