han.holl@xxxxxxxxxxxxxxxxxxxx wrote:
Now the query:
select item from aview where exp > 0 and cheap > 0;
will lead to a sequential scan on atable with filter:
very_expensive_function(item) > 0 and cheap_function(item) > 0
The query would run much faster with the filter reordered.
Is there a way to tell the planner/optimizer that certain functions are more
expensive than others, and should be postponed in lazy evaluation ?
Or is there a hook in the system that would allow me too look at and maybe
reorder expressions before they are executed ?
Not really. Perhaps look into using a functional/expressional index and
see if that does the job for you.
http://www.postgresql.org/docs/8.2/static/indexes-expressional.html
http://www.postgresql.org/docs/8.2/static/sql-createfunction.html
--
Richard Huxton
Archonet Ltd
