EXISTS Is Self-Contained

Shane O’Neill ponders an existential problem:

So, drinking my first (of many) coffee of the day, I asked him what was wrong with it.

I have two tables. 1 with values 1,2,3 & the other with values 1,2,3,4,5. When I use delete exists, it should just delete 1,2,3 but table1 is always empty.

Hmmm, not an unreasonable assumption I suppose so I asked him for his code.

Read on for Shane’s explanation, though he doesn’t like the verbosity.  My version is, what happens in EXISTS stays in EXISTS.  It just returns a signal to the outer query saying yea or nay and the outer query does its thing accordingly.  In this case, if you want to tie results back to the delete operation, use IN (the ANSI standard way) or JOIN (typically my preferred way, given that IN can get dicey with more complex criteria).

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