Re: Understanding sequential versus index scans.

PS Running "PostgreSQL 8.2.1 on i686-pc-mingw32, compiled by GCC gcc.exe
(GCC) 3.4.2 (mingw-special)"

On Sun, Jul 19, 2009 at 6:58 PM, Robert James <srobertjames(at)gmail(dot)com>wrote:

> Hi. I notice that when I do a WHERE x, Postgres uses an index, and when I
> do WHERE y, it does so as well, but when I do WHERE x OR y, it doesn't. Why
> is this so? And how can I shut this off?
> select * from dict
> where
> word in (select substr('moon', 0, generate_series(3,length('moon')))) --
> this is my X above
> OR word like 'moon%' -- this is my Y above
>
> Seq Scan on dict (cost=0.02..2775.66 rows=30422 width=24) (actual
> time=16.635..28.580 rows=8 loops=1)
> Filter: ((hashed subplan) OR ((word)::text ~~ 'moon%'::text))
> SubPlan
> -> Result (cost=0.00..0.01 rows=1 width=0) (actual time=0.014..0.019
> rows=2 loops=1)
> Total runtime: 28.658 ms
> (Using just X or Y alone uses the index, and completes in 0.150 ms)
> Is this a bug?
>
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