>Normally EXISTS is used in situations where you need to correlate one table with another. In your case where is no correlation, so the above is better written as
>

>if exists(select 1 from ForumCli where NoMember = 1 and NoClient IN (1,2))
>
>   select Numero from Thread where NoStatus = 1
>
>else
>
>    select Numero from Thread where 1=0 -- to produce empty result

There is always at least one child record as per that condition. But, thanks for mentioning it.