Saturday, August 4, 2012
Today I learnt something new in SQL Queries..
Thot I could share with you ppl!
I was running
query a (select col1 from table1)>> execution time 3 secs
query b (select col1 from table2)>> execution time 5 secs
query a intersect query b
(select col1 from table1 intersect select col1 from table2)>> execution time 16 mins!
Lot of technicalities and reasons are there for this behavior... but quick fix is as follows
select col1 from table1 where rownum>0
intersect
select col1 from table2 where rownum>0 >> execution time 6 secs!
Labels: Programming
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2 comments:
Very Nice article, thank u
Sounds like the intersect wasn't using hashing to generate the intersection. Probably better to use an inner join in this case.
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