SQL help with EXISTS

I am pretty sure that the following selected only a few records from a large file (ASHPNBR = 'BN123456' ).

Then I changed a paren or something small and I cant get it to select only a few records - now it selects ALL values of ASHPNBR.

The sub-select works great and only selects a few records.

When I add the outer select, the entire file is selected (all ASHPNBR values).

How does EXISTS know which keys to join between the inner & outer query? Do I have to explicitly state the join? Or does "EXISTS" make assumption about which fields to join?

Thanks







select * from miscchg A
where
exists
(select ASHPNBR, ABLDNGD, AMSCHRG from MISCCHG
where
ASHPNBR = 'BN123456'
group by ASHPNBR,ABLDNGD, AMSCHRG )

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