Help on query plan. (was: select like and indexes)

   Well guys,

     I made a search on the archives and found a message on my issue.
It's subject is: "Why won't the query planner use my index?".

     There was a suggestion of setting 'enable_seqscan' to off to see
whether the query planner was chosing the right way or not.

     Here goes my results:

access=# explain analyze select * from tbl_access where ip like '12%157';
                                                     QUERY PLAN
-------------------------------------------------------------------
  Seq Scan on tbl_access  (cost=0.00..42519.84 rows=139 width=134)
(actual time=698.03..20504.07 rows=1391 loops=1)
    Filter: (ip ~~ '12%157'::text)
  Total runtime: 20507.44 msec
(3 rows)

-------------------------------------------------------------------

access=# SET enable_seqscan = off;
SET
access=# explain analyze select * from tbl_access where ip like '12%157';
                                                     QUERY PLAN

-------------------------------------------------------------------
  Index Scan using teste1 on tbl_access  (cost=0.00..63593.03 rows=139
width=134) (actual time=160.69..1177.26 rows=1391 loops=1)
    Index Cond: ((ip >= '12'::character varying) AND (ip <
'13'::character varying))
    Filter: (ip ~~ '12%157'::text)
  Total runtime: 1181.18 msec
(4 rows)


--------------------------------------------------------------------

   Well, although PG is chosing for a Sequential Scan, the Index Scan
showed to be much more faster.

   Is that a problem with the planner or a normal behavior?

william

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