>>As I know there is SELECT's filter using EXIST, which format is:
>>SELECT <...> WHERE EXIST (subquery)
>>
>>How to use it? I have found very little information about it
>>in VFP Help. I have tried it with 2 tables with diferent fields,
>>but didn't work. :(
>
>SELECT SomeField FROM TableA WHERE ExtKey EXIST IN
>(SELECT Key FROM TableB)

There is no "EXIST IN" condition for SELECT-SQL. There is "EXISTS" and "IN", but you cannot combine them.

Vlad