Re: constraints in query plans

On Sun, 2006-10-15 at 20:36 -0700, Jeremy Drake wrote:
> I just tried that,
> CREATE INDEX test_domain_k_x1_x2_mp ON test_domain (k, x1, x2, mp);
> 
> and dropped the others.  That actually works properly.
> jeremyd=# explain analyze select * from test_domain where k = 1255 and mp;
>                                                             QUERY PLAN
>
----------------------------------------------------------------------------------------------------------------------------------
>  Bitmap Heap Scan on test_domain  (cost=5.37..237.21 rows=66 width=17) (actual time=0.115..0.707 rows=132 loops=1)
>    Recheck Cond: (k = 1255)
>    Filter: mp
>    ->  Bitmap Index Scan on test_domain_k_x1_x2_mp  (cost=0.00..5.37 rows=66 width=0) (actual time=0.081..0.081
rows=132loops=1)
 
>          Index Cond: ((k = 1255) AND (mp = true))
>  Total runtime: 1.137 ms
> (6 rows)
> 
> I thought I had to refer to all of the columns in order for this to work,
> that I could not skip some in the middle, but it seems to work.
> 

As long as "k=1255" is selective enough, the index is useful. That's
because k is the first item in the index key.

Regards,Jeff Davis