>Thank you. I am trying to also understand why the EXISTS needs the expression T1.PK_FLD = T2.PK_FLD in subquery and according to Naomi the WHERE IN does not need it. But your use of 1 should make the subquery run faster.
>
>PS. If this is a duplicate post, I apologize. UT just crashed on me.
>

It crashed for me too today a few times.

As I said in my other message, there is absolutely no difference in using EXISTS (select 1 ...)
or EXISTS (select * ...)

In WHERE IN we don't need an expression because IN actually selects all the values. The EXISTS subquery just tests and exits as soon as it finds a value satisfying the condition. So EXISTS may perform faster than IN in addition of possible problems associated with IN which you don't have when using EXISTS.