[SQL] posgres optimizer not using the index on hstore HELP

[adam]

I have a simple query select on the hstore attribute "EMAIL_ADDRESS". but the
thing is i'm using a parameter in the query to specify which hstore
attribute I want to access, and when using a parameter the index which I
created is suppressed; whereas when I hard code the attribute
"EMAIL_ADDRESS" then the index is used. this is the index I created:

create index indx_email on contact using btree
((contact_attributes->'EMAIL_ADDRESS'::text));


the query is:

select * from contact where contact_attributes->$parameter =
"fqw...@hotmail.com';


when I hardcode the attribute like below it the index is used.

select * from contact where contact_attributes->'EMAIL_ADDRESS' =
"fqw...@hotmail.com';



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[Steve Midgley]

On Mon, Jul 18, 2016 at 8:18 AM, adam <adha...@hotmail.com> wrote:

I have a simple query select on the hstore attribute "EMAIL_ADDRESS". but the
thing is i'm using a parameter in the query to specify which hstore
attribute I want to access, and when using a parameter the index which I
created is suppressed; whereas when I hard code the attribute
"EMAIL_ADDRESS" then the index is used. this is the index I created:

create index indx_email on contact using btree
((contact_attributes->'EMAIL_ADDRESS'::text));


the query is:

select * from contact where contact_attributes->$parameter =
"fqw...@hotmail.com';


when I hardcode the attribute like below it the index is used.

select * from contact where contact_attributes->'EMAIL_ADDRESS' =
"fqw...@hotmail.com';

Maybe you can share an EXPLAIN ANALYZE for both queries?

Steve 

[Tom Lane]

adam <adha...@hotmail.com> writes:
> I have a simple query select on the hstore attribute "EMAIL_ADDRESS". but the
> thing is i'm using a parameter in the query to specify which hstore
> attribute I want to access, and when using a parameter the index which I
> created is suppressed; whereas when I hard code the attribute
> "EMAIL_ADDRESS" then the index is used.

WFM:

regression=# create extension hstore;
CREATE EXTENSION
regression=# create table foo(f1 hstore);
CREATE TABLE
regression=# create index on foo ((f1->'bar'));
CREATE INDEX
regression=# explain select * from foo where f1->'bar' = 'baz';
QUERY PLAN
---------------------------------------------------------------------------
Bitmap Heap Scan on foo (cost=4.21..14.37 rows=7 width=32)
Recheck Cond: ((f1 -> 'bar'::text) = 'baz'::text)
-> Bitmap Index Scan on foo_expr_idx (cost=0.00..4.21 rows=7 width=0)
Index Cond: ((f1 -> 'bar'::text) = 'baz'::text)
(4 rows)

regression=# prepare p as select * from foo where f1->$1 = $2;
PREPARE
regression=# explain execute p('bar', 'baz');
QUERY PLAN
---------------------------------------------------------------------------
Bitmap Heap Scan on foo (cost=4.21..14.37 rows=7 width=32)
Recheck Cond: ((f1 -> 'bar'::text) = 'baz'::text)
-> Bitmap Index Scan on foo_expr_idx (cost=0.00..4.21 rows=7 width=0)
Index Cond: ((f1 -> 'bar'::text) = 'baz'::text)
(4 rows)

As a general rule, when you haven't mentioned the PG version you're using
nor provided an *exact* example of what you're doing, it's difficult to
offer useful help.

regards, tom lane