>When you don't use LEFT JOIN but just EXISTS conditions, how many ClientID satisfy that criteria?

I have 537 records with the LEFT JOIN and 537 records without them. But, that is with the full EXISTS syntax. The IS NULL approach does not give the same amount of records. If I replace the full EXISTS syntax with the IS NULL approach, I get 697 records.

>Do you want to get all these clients information along with extra columns from other tables joined based on that ClientID ?

Yes