Re: Inlining of functions (doing LIKE on an array)

"ldh@laurent-hasson.com" <ldh@laurent-hasson.com> writes:
> I tried "exists", but won't work in the Function, i.e.,
> CREATE OR REPLACE FUNCTION ArrayLike(text[], text) RETURNS bigint
>   AS  'exists (select * from unnest($1) a where a like $2)'
> LANGUAGE SQL STRICT IMMUTABLE LEAKPROOF

Syntax and semantics problems.  This would work:

regression=# CREATE OR REPLACE FUNCTION ArrayLike(text[], text) RETURNS bool
regression-# as 'select exists (select * from unnest($1) a where a like $2)'
regression-# LANGUAGE SQL STRICT IMMUTABLE;
CREATE FUNCTION
regression=# create table tt (f1 text[]);
CREATE TABLE
regression=# explain select * from tt where ArrayLike(f1, 'foo');
                      QUERY PLAN
-------------------------------------------------------
 Seq Scan on tt  (cost=0.00..363.60 rows=453 width=32)
   Filter: arraylike(f1, 'foo'::text)
(2 rows)

But we don't inline SQL functions containing sub-selects, so you're still
stuck with the rather high overhead of a SQL function.  A plpgsql function
might be a bit faster:

CREATE OR REPLACE FUNCTION ArrayLike(text[], text) RETURNS bool
as 'begin return exists (select * from unnest($1) a where a like $2); end'
LANGUAGE plpgSQL STRICT IMMUTABLE;

BTW, I'd be pretty suspicious of marking this function leakproof,
because the underlying LIKE operator isn't leakproof according to
pg_proc.


> It's as expected though. As for the GIN indices, I tried and it didn't make a difference, which I guess is expected
aswell because of the Like operator. I don't expect regular indices to work on regular columns for Like operations,
especially'%xxx' ones, so I didn't expect GIN indices to work either for Array columns with Like. Am I wrong? 

Plain GIN index, probably not.  A pg_trgm index could help with LIKE
searches, but I don't think we have a variant of that for array columns.

Have you considered renormalizing the data so that you don't have
arrays?

            regards, tom lane