These are two confusing issues.
One is the use of a leading percent sign.
What Tom pointed out was with a bound parameter the planner can't
make any assumptions about indexes.
Leading percent signs can be made to use indexes by creating a
functional index on the column which reverses the order of the
column, then using the same function in the select
Dave
On 25-May-06, at 1:46 PM, Andrew Sullivan wrote:
On Thu, May 25, 2006 at 02:18:10PM -0300, Rodrigo Hjort wrote:
make a index scan. Otherwise, i.e. using leading '%' on static
text or bound
paremeter, makes the planner always do a sequential scan. Is that the
scenario?
I think more exactly, the planner can't possibly know how to plan an
indexscan with a leading '%', because it has nowhere to start.
Think of it this way: if you go to the public library, and say, "I
want a book. I can't remember its name exactly, but it starts with
'daytime'," you can find it by going to the title index and browsing
for things that start that way. If you go to the public library, and
say, "There's this book I want, but I can't remember the title. It's
red," you're going to have a lot of books to look through. Maybe all
of them.
If it were important enough -- say you left a $10,000 cheque inside
-- you might just start looking. Maybe you'll get lucky, and hit
it.
A
--
Andrew Sullivan | [EMAIL PROTECTED]
I remember when computers were frustrating because they *did*
exactly what
you told them to. That actually seems sort of quaint now.
--J.D. Baldwin
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broadcast)---------------------------
TIP 6: explain analyze is your friend
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TIP 6: explain analyze is your friend
