Hackers,
I'm trying to write a query to give me a list of the columns and/or expressions in an index. For example, given this
table:
david=# \d foo Table "public.foo"Column | Type | Modifiers
---------+-----------+-----------id | integer | bar_ids | integer[] |
Indexes: "idx_foo_stuff" btree (id, abs(id), (bar_ids[1]))
I'd like to write a query to emit:
i | coalesce
---+---------------------0 | id1 | abs(id)2 | bar_ids[1]
However, it looks as if I can only get multiple expressions as a single string. The query I've come up with is:
SELECT s.i, COALESCE(a.attname, pg_catalog.pg_get_expr( x.indexprs, ct.oid )) FROM pg_catalog.pg_index
x JOIN pg_catalog.pg_class ct ON ct.oid = x.indrelid JOIN pg_catalog.pg_class ci ON ci.oid =
x.indexrelid JOIN pg_catalog.pg_namespace n ON n.oid = ct.relnamespace JOIN generate_series(0,
current_setting('max_index_keys')::int- 1) s(i) ON x.indkey[s.i] IS NOT NULL LEFT JOIN
pg_catalog.pg_attributea ON ct.oid = a.attrelid AND a.attnum = x.indkey[s.i] WHERE ct.relname
='foo' AND ci.relname = 'idx_foo_stuff' AND n.nspname = 'public' ORDER BY s.i;
Which emits:
i | coalesce
---+---------------------0 | id1 | abs(id), bar_ids[1]2 | abs(id), bar_ids[1]
Is there some way to only get the relevant index expression from indexprs, rather than the whole expression?
Thanks,
David
PS: I need this to work all the way back to 8.1, if possible.
