On Tue, May 02, 2006 at 01:37:54PM +0200, Markus Schiltknecht wrote: > Hi, > > when using LIMIT, how do I tell the planner to only call a function for > rows it returns? > > An example: I want to fetch the top five categories. A function > get_category_text_path(cat_id int) returns the textual representation of > the category. For that I do something like: > > SELECT id, get_category_text_path(id) > FROM category > ORDER BY rank > LIMIT 5
How about:
SELECT id, get_category_text_path(id)
FROM (SELECT id FROM category
ORDER BY rank
LIMIT 5) as x;
Evidently you don't have an index on rank, otherwise it would've used
the index to cut down on the number of rows that needed to be examined.
Have a nice day,
--
Martijn van Oosterhout <kleptog@svana.org> http://svana.org/kleptog/
> From each according to his ability. To each according to his ability to
> litigate.
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