From: | Francisco Reyes <lists(at)natserv(dot)com> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | Francisco Reyes <lists(at)natserv(dot)com>, Pgsql Novice <pgsql-novice(at)postgresql(dot)org> |
Subject: | Re: Index not used on single select, but used in join. |
Date: | 2001-11-07 23:36:21 |
Message-ID: | 20011107182428.H27009-100000@zoraida.natserv.net |
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Thread: | |
Lists: | pgsql-novice |
> Seems to work for me:
>
> regression=# create table hraces (horse text);
> CREATE
> regression=# create index hri on hraces(lower(horse));
> CREATE
> regression=# explain select horse from hraces where lower(horse) = 'little irish nut';
> NOTICE: QUERY PLAN:
>
> Index Scan using hri on hraces (cost=0.00..17.08 rows=5 width=32)
>
> EXPLAIN
>
> What does EXPLAIN actually show for you?
drf=# explain select horse from hraces where lower(horse) = 'little irish
nut';
NOTICE: QUERY PLAN:
Seq Scan on hraces (cost=0.00..208976.96 rows=75793 width=12)
EXPLAIN
> If you try to force an
> indexscan by doing "SET enable_seqscan TO off", does the EXPLAIN
> result change?
yes.
drf=# SET enable_seqscan TO off;
SET VARIABLE
drf=# explain select horse from hraces where lower(horse) = 'little irish
nut';
NOTICE: QUERY PLAN:
Index Scan using hr_lhorse on hraces (cost=0.00..223420.22 rows=75793
width=12)
EXPLAIN
>Have you VACUUM ANALYZEd the table recently?
Yes. Did it after I created the index.
What implication is there on leaving the enable_seqscan to Off?
Just as a test I am running VACUUM ANALYZE again
Another piece of info. I have another table where I also have an index on
lower(horse) and that works fine. That table though is only about 500,000
rows.
General question. After creating an index is it advasible to run a VACUUM
ANALYZE?
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