As always, a very good and educative answer, Adam. I just think that
the LEFT JOIN part is incorrect this time:

> Using Left Join:
>
> select *
> from clientes C
> left join vendas v on (V.cli_cod=C.cli_cod)
> where V.cli_cod IS NOT NULL
> and V.vnd_data BETWEEN '2006-1-01' AND '2006-1-31';

To me this seems like an ordinary inner JOIN. Shouldn't it be

select *
from clientes C
left join vendas v on (V.cli_cod=C.cli_cod
and V.vnd_data BETWEEN '2006-1-01' AND '2006-1-31')
where V.cli_cod IS NULL

i.e. put all things that's part of the record that shouldn't exist in
the JOIN clause, and then just the IS NULL in the WHERE clause to
ascertain there ain't any such records.

Myself, I find the NOT EXISTS solution to be the easiest to understand
and quickest to execute, so I don't use IN (<subselect>) or LEFT JOIN
... WHERE <right table PK> IS NULL unless there is a very good reason.

Set