Hi every1,

I'm using NOT IN inside my SQL query.

For example:

select columnA 
from table1
where columnA not in (
select columnB
from table2)

How is it possible that this part of the query

select columnB
from table2

takes 30sec to complete, but the whole query above takes 0.1sec to complete?? Shouldn't the complete query take 30sec + ?

BTW, both queries return valid results.

Thanks!

Answers to Comments

Is it because the second query hasn't actually completed but has only returned back the first 'x' rows (out of a very large table?)

No, the query is completed after 30 seconds, not to many rows returned (eg. 50).

But @Aleksandar wondered why the question congaing the performance killer was so fast.

my point exactly

Also how long does select distinct columnB from table2 take to execute?

actually, the original query is "select distinct...