Re: programmatically retrieve details of a custom Postgres type

pá 11. 11. 2022 v 5:02 odesílatel Konstantin Izmailov <pgfizm(at)gmail(dot)com>
napsal:

> Hello,
> I was unable to find how to get column names, sizes and types for a given
> composite type.
>
> Example. For a type defines as:
> CREATE TYPE inventory_item AS (
> name text,
> supplier_id integer,
> price numeric
> );
>
> I have a plpgsql stored proc that returns SETOF inventory_item (i.e. there
> is no table with a column of this type).
>
> I looked into the pg_type table but it only contains oid and typrelid for
> the inventory_item type. I need a query that returns information about
> structure of the composite type, i.e.:
> ColumnName | ColumnType | ColumnSize
> name | text | -1
> supplier_id | integer | 4
> price | numeric | 16
>
> Is this possible? I'm executing queries via libpq...
>

(2022-11-11 05:06:26) postgres=# create type foo as (a int, b varchar, c
numeric);
CREATE TYPE
(2022-11-11 05:06:42) postgres=#
\q
[pavel(at)localhost isolation]$ psql -E
Assertions: on
psql (16devel)
Type "help" for help.

(2022-11-11 05:06:47) postgres=# \d foo
********* QUERY **********
SELECT c.oid,
n.nspname,
c.relname
FROM pg_catalog.pg_class c
LEFT JOIN pg_catalog.pg_namespace n ON n.oid = c.relnamespace
WHERE c.relname OPERATOR(pg_catalog.~) '^(foo)$' COLLATE pg_catalog.default
AND pg_catalog.pg_table_is_visible(c.oid)
ORDER BY 2, 3;
**************************

********* QUERY **********
SELECT c.relchecks, c.relkind, c.relhasindex, c.relhasrules,
c.relhastriggers, c.relrowsecurity, c.relforcerowsecurity, false AS
relhasoids, c.relispartition, '', c.reltablespace, CASE WHEN c.reloftype =
0 THEN '' ELSE c.reloftype::pg_catalog.regtype::pg_catalog.text END,
c.relpersistence, c.relreplident, am.amname
FROM pg_catalog.pg_class c
LEFT JOIN pg_catalog.pg_class tc ON (c.reltoastrelid = tc.oid)
LEFT JOIN pg_catalog.pg_am am ON (c.relam = am.oid)
WHERE c.oid = '16389';
**************************

********* QUERY **********
SELECT a.attname,
pg_catalog.format_type(a.atttypid, a.atttypmod),
(SELECT pg_catalog.pg_get_expr(d.adbin, d.adrelid, true)
FROM pg_catalog.pg_attrdef d
WHERE d.adrelid = a.attrelid AND d.adnum = a.attnum AND a.atthasdef),
a.attnotnull,
(SELECT c.collname FROM pg_catalog.pg_collation c, pg_catalog.pg_type t
WHERE c.oid = a.attcollation AND t.oid = a.atttypid AND a.attcollation
<> t.typcollation) AS attcollation,
a.attidentity,
a.attgenerated
FROM pg_catalog.pg_attribute a
WHERE a.attrelid = '16389' AND a.attnum > 0 AND NOT a.attisdropped
ORDER BY a.attnum;
**************************

Composite type "public.foo"
┌────────┬───────────────────┬───────────┬──────────┬─────────┐
│ Column │ Type │ Collation │ Nullable │ Default │
╞════════╪═══════════════════╪═══════════╪══════════╪═════════╡
│ a │ integer │ │ │ │
│ b │ character varying │ │ │ │
│ c │ numeric │ │ │ │
└────────┴───────────────────┴───────────┴──────────┴─────────┘

Important part is:

(2022-11-11 05:08:20) postgres=# select attname, atttypid::regtype from
pg_attribute where attrelid = 'foo'::regclass;
┌─────────┬───────────────────┐
│ attname │ atttypid │
╞═════════╪═══════════════════╡
│ a │ integer │
│ b │ character varying │
│ c │ numeric │
└─────────┴───────────────────┘
(3 rows)

> Thank you!
>

Regards

Pavel