postgresql index id

1postgres@db # SELECT a.attname
2FROM pg_class t
3     JOIN pg_index ix ON t.oid = ix.indrelid
4     JOIN pg_class i ON i.oid = ix.indexrelid
5     JOIN pg_attribute a ON a.attrelid = t.oid
6WHERE 
7     a.attnum = ANY(ix.indkey) AND 
8     t.relkind = 'r' AND 
9     t.relname ='test' -- table name
10ORDER BY
11     t.relname,
12     i.relname;
13 attname 
14---------
15 column1
16 column2
17 id
18(3 rows)
19