SQL - query inside NOT IN takes longer than the complete query ??
- by Aleksandar Tomic
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...