Re: Join on incompatible types

>>>>> "Shridhar" == Shridhar Daithankar <shridhar_daithankar(at)myrealbox(dot)com> writes:

Shridhar> Laurent Martelli wrote:
>>>>>>> "Shridhar" == Shridhar Daithankar
>>>>>>> <shridhar_daithankar(at)myrealbox(dot)com> writes:
Shridhar> Laurent Martelli wrote:
>> [...] >> Should I understand that a join on incompatible types
>> (such as >> integer and varchar) may lead to bad performances ?
Shridhar> Conversely, you should enforce strict type compatibility
Shridhar> in comparisons for getting any good plans..:-)
>> Ha ha, now I understand why a query of mine was so sluggish. Is
>> there a chance I could achieve the good perfs without having he
>> same types ? I've tried a CAST in the query, but it's even a
>> little worse than without it. However, using a view to cast
>> integers into varchar gives acceptable results (see at the end).
>> I'm using Postgresql 7.3.4.

Shridhar> I am stripping the analyze outputs and directly jumping to
Shridhar> the end.

Shridhar> Can you try following?

Shridhar> 1. Make all fields integer in all the table.

I can't do this because lists.values contains non integer data which
do not refer to a classes.id value. It may sound weird. This is
because it's a generic schema for a transparent persistence framework.

The solution for me would rather be to have varchar everywhere.

Shridhar> 2. Try following query EXPLAIN ANALYZE SELECT * from lists
Shridhar> join classes on classes.id=lists.value where
Shridhar> lists.id='16'::integer;

Shridhar> How does it affect the runtime?

Shridhar> Shridhar

--
Laurent Martelli
laurent(at)aopsys(dot)com Java Aspect Components
http://www.aopsys.com/ http://jac.aopsys.com