On 2/4/25 08:23, Henning Garus wrote:
Hi,
I stumbled upon this behaviour when digging into the performance of some
merge statements generated by hibernate.
Looking at different String types (varchar, text and bpchar) in some
cases an index is used when the index type differs from the type in the
query, in some cases it isn't used.
Given a table with an index on a bpchar column:
create table test (id bpchar(8) primary key);
Both of the following queries use the index:
explain select * from test where id = 'foo'::bpachar(3);
explain select * from test where id = 'foo'::varchar;
However when the String is cast to text the index isn't used:
explain select * from test where id = 'foo'::text;
The output from EXPLAIN ANALYZE on each of the queries would be useful.
This behavior seems to be consistent across postgres 12, 16 and 17.
I find it surprising that the cast to varchar behaves differently than
the cast to text, is this intended behaviour?
Cheers
Henning
--
Adrian Klaver
adrian.klaver@xxxxxxxxxxx
