How to Use Exists Clause

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Michael Earl-395764 SSC Guru Points: 53873 More actions · Answer 1

Performance will not make a difference, but they can return different results.

If the field you reference when not using * returns all NULL values, even if there are rows in the table, the EXISTS will be false.

Gunjan Hall of Fame Points: 3226 More actions · Answer 2

Thanks.

But it will be good if my next statements will be based upon that field.

Then it will improve the perfomance...

right??

Thanks.

Gunjan.

Gunjan Hall of Fame Points: 3226 More actions · Answer 3

I checked..

Even if the field is NULL it returns the "True" in EXISTS statement...

Thanks.

Gunjan.

Michael Earl-395764 SSC Guru Points: 53873 More actions · Answer 4

I am not sure what you meant by this:

[font="Courier New"]But it will be good if my next statements will be based upon that field.

Then it will improve the perfomance...

right?? [/font]

but the EXISTS performance will be the same either way.

You can, of course, just look at the execution plans - this is pretty easy to test.

khelangandhi Valued Member Points: 73 More actions · Answer 5

If you know that you are looking for single field from the table...the definately you should go for if Exists(Select Specialty from Doctors)

Gunjan Hall of Fame Points: 3226 More actions · Answer 6

Khelan I think you didn't got the question....

Its about performace.......

which is better one??

Thanks.

Gunjan.