Check if a user-defined type already exists in PostgreSQL

Question

Say I have created some user-defined types in the DB,

i.e. CREATE TYPE abc ...

Is it then possible to determine if the user-defined type exists

Answer 1

I'm trying to do the same thing, ensure a type exists.

I started psql with the --echo-hidden (-E) option and entered \dT:

$ psql -E
psql (9.1.9)
testdb=> \dT
********* QUERY **********
SELECT n.nspname as "Schema",
  pg_catalog.format_type(t.oid, NULL) AS "Name",
  pg_catalog.obj_description(t.oid, 'pg_type') as "Description"
FROM pg_catalog.pg_type t
     LEFT JOIN pg_catalog.pg_namespace n ON n.oid = t.typnamespace
WHERE (t.typrelid = 0 OR (SELECT c.relkind = 'c' FROM pg_catalog.pg_class c WHERE c.oid = t.typrelid))
  AND NOT EXISTS(SELECT 1 FROM pg_catalog.pg_type el WHERE el.oid = t.typelem AND el.typarray = t.oid)
      AND n.nspname <> 'pg_catalog'
      AND n.nspname <> 'information_schema'
  AND pg_catalog.pg_type_is_visible(t.oid)
ORDER BY 1, 2;
**************************
 List of data types
 Schema |       Name       | Description 
--------+------------------+-------------
 public | errmsg_agg_state | 
(1 row)

If you are using schemas and search_path (I am) then you'll probably need to keep the pg_catalog.pg_type_is_visible(t.oid) check. I don't know what all the conditions in the WHERE are doing, but they didn't seem relevant to my case. Currently using:

SELECT 1 FROM pg_catalog.pg_type as t
   WHERE typname = 'mytype' AND pg_catalog.pg_type_is_visible(t.oid);

Answer 2

You can look in the pg_type table:

select exists (select 1 from pg_type where typname = 'abc');

If that is true then abc exists.

Answer 3

Indeed, Postgres does not have CREATE OR REPLACE functionality for types. So the best approach is to drop it:

DROP TYPE IF EXISTS YOUR_TYPE;
CREATE TYPE YOUR_TYPE AS (
    id      integer,
    field   varchar
);

Simple solution is always the best one.

Answer 4

-- All of this to create a type if it does not exist
CREATE OR REPLACE FUNCTION create_abc_type() RETURNS integer AS $$
DECLARE v_exists INTEGER;

BEGIN
    SELECT into v_exists (SELECT 1 FROM pg_type WHERE typname = 'abc');
    IF v_exists IS NULL THEN
        CREATE TYPE abc AS ENUM ('height', 'weight', 'distance');
    END IF;
    RETURN v_exists;
END;
$$ LANGUAGE plpgsql;

-- Call the function you just created
SELECT create_abc_type();

-- Remove the function you just created
DROP function create_abc_type();
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