How does postgres behave if several indexes have (nearly) identical conditions?

[Koen De Groote]

Greetings all.

Example table:

CREATE TABLE my_table (
    id serial PRIMARY KEY,
    a001 BOOLEAN default 't',
    a002 BOOLEAN default 'f',
    a003 BOOLEAN default 't',
    a004 BOOLEAN default 'f'
);

And these 2 indexes:

create index index_001 on my_table using btree (a001,a002,a003) where
a001=true and a002=false;

create index index_002 on my_table using btree (a003) where a001=true and
a002=false;

Now take this query:

select * from my_table where a001=true;

Which index will postgres pick? I'm wondering how postgres goes about
picking an index to consider.

And if it will consider others if the analysis of the first says a seqscan
would be better than the index it first considered?

Regards,
Koen De Groote