select
t.relname as table_name,
i.relname as index_name,
a.attname as column_name,
pg_size_pretty(pg_relation_size(quote_ident(i.relname)::text)) AS index_size
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.relname = 'trainings'
order by
t.relname,
i.relname;