2011/6/5 Håvard Wahl Kongsgård
<haavard.kongsgaard@gmail.com> Hi, my database performance badly on substring comparison between two very large tables. In postgresql 8.4 is it possible to create a index on a substring, or must I create an new field for the substring match ( and then create a new index for that field)?
Hi,
I've checked that for 9.0, however for 8.4 should work as well:
CREATE INDEX i_test_sbstr ON test( substring(t, 5, 3) );
It is important that the substring() parameters in the index definition are the same as you use in your query.
regards
Szymon