Thanks for the reply.
(i'm sorry for that i didn't really know how to reply to a certain message...)
well, i used LIKE, but i actually wanted just "starts with".
the solution i found without using LIKE is this:
CREATE OR REPLACE FUNCTION test_func(STR text)
RETURNS integer AS
$BODY$
declare
STR2 varchar;
begin
-- example: if STR is 'abc' then STR2 would be 'abd'
STR2 := substring(STR,0,length(STR))||chr((ascii(substring(STR,length(STR)))+1));
insert into plcbug(val) values('begin time before perform');
perform t1.val FROM t1 WHERE
(COALESCE(rpad((val)::text, 100, ' '::text), ''::text) ~>=~ STR::text) AND
(COALESCE(rpad((val)::text, 100, ' '::text), ''::text) ~<~ STR2::text)
order by COALESCE(rpad(t1.val, 100), '') using ~<~ LIMIT 5;
insert into plcbug(val) values('time after perform');
return 1;
END;
$BODY$
LANGUAGE plpgsql VOLATILE
COST 100;
ALTER FUNCTION test_func(text) OWNER TO postgres;
1. is there any more elegant solution?
2. considering LIKE, practically there are only two cases: the _expression_ (variable||'%') may be '%something%' or 'something%' [*], right?? do you think the optimizer can do better by conditionally splitting the plan according to actual value of a variable?
[*] for the sake of the discussion lets forget about '_something'.
Thanks again.
On Tue, Aug 16, 2011 at 16:40, Tom Lane <tgl@xxxxxxxxxxxxx> wrote:
> ...
> perform t1.val FROM t1 WHERE[ doesn't use index ]
> (COALESCE(rpad(t1.val, 100),'') ) like COALESCE(STR || '%','')
> order by COALESCE(rpad(t1.val, 100), '') using ~<~ LIMIT 5;
No, it doesn't. The LIKE index optimization requires the LIKE pattern
to be a constant at plan time, so that the planner can extract the
pattern's fixed prefix. An _expression_ depending on a function parameter
is certainly not constant.
If you really need this to work, you could use EXECUTE USING so that
the query is re-planned for each execution.
regards, tom lane
