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!

2 comments:

Naveed Ayub said...

Very Nice article, thank u

Micro Paywall said...

Sounds like the intersect wasn't using hashing to generate the intersection. Probably better to use an inner join in this case.