query plan ignoring check constraints

(n-1)*10000<id<n*10000 subtable_n

 

Additionally, I have created check constraints for each table as per their range. So subtable_i can contain ids only in the range (i-1)*10000 < id < i*10000 . The check constraints work well when i try to insert a value outside the range by disallowing such inserts. Each of the subtables have been indexed on id.

 

Now, when I do a select on the basetable with a range of ids, it looks up each subtable that inherits from the base table and using an indexed scan searches for values in the range. It does it even for subtables whose check constraint completely rules out the possibility of it containing any such row . Should not check constraint act as the first filter? The index should ideally be scanned only when the check constraint is passed by the search criteria but surprisingly it did not happen. The explain analyze showed cost for index scans of subtables that cannot contain rows matching the search criteria.

 

Is there any way I can enforce this or is there any other way of hinting  the query planner to completely ignore looking at a subtable for a given range/criteria?

 

Thanks,

Rohit