Strange indexing

Started by Uros Gruberalmost 24 years ago2 messagesgeneral
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#1Uros Gruber
uros@sir-mag.com

Hi!

is this OK.

CREATE TABLE test (
id int primary key,
name varchar(255),
parent varchar(32)
);

If i write

explain select * from test where id=1;

This is output of 1st table:
Index Scan using test_pkey on test (cost=0.00..4.82 rows=1 width=183)

but the i create index on parent like this

create index tt on test (parent);

And when i execute query

explain select * from test where parent = '1';

Seq Scan on test (cost=0.00..1.07 rows=1 width=17)

Why i there no index scan if i create index. I also run
vacuum on this table.

both queryes return only 1 row.

--
bye,
Uros mailto:uros@sir-mag.com

#2Tom Lane
tgl@sss.pgh.pa.us
In reply to: Uros Gruber (#1)
Re: Strange indexing

Uros Gruber <uros@sir-mag.com> writes:

explain select * from test where parent = '1';
Seq Scan on test (cost=0.00..1.07 rows=1 width=17)

Why i there no index scan if i create index. I also run
vacuum on this table.

After the vacuum, the planner knows that your table is too small to
bother with an indexscan. Try putting in a more realistic amount of
data.

regards, tom lane