List columns with indexes in PostgreSQL

Question

I would like to get the columns that an index is on in PostgreSQL.

In MySQL you can use SHOW INDEXES FOR table and look at the Column_name

Answer 1

If you want to preserve column order in the index, here's a (very ugly) way to do that:

select table_name,
    index_name,
    array_agg(column_name)
from (
    select
        t.relname as table_name,
        i.relname as index_name,
        a.attname as column_name,
        unnest(ix.indkey) as unn,
        a.attnum
    from
        pg_class t,
        pg_class i,
        pg_index ix,
        pg_attribute a
    where
        t.oid = ix.indrelid
        and i.oid = ix.indexrelid
        and a.attrelid = t.oid
        and a.attnum = ANY(ix.indkey)
        and t.relkind = 'r'
        and t.relnamespace = 
    order by
        t.relname,
        i.relname,
        generate_subscripts(ix.indkey,1)) sb
where unn = attnum
group by table_name, index_name

column order is stored in the pg_index.indkey column, so I ordered by the subscripts from that array.