Cannot cast to type alias

Question

I created a type alias gp for the PostgreSQL type money , and I can't figure out from the documentation how I'm supposed to use this.

I've set up a test table (and database):

CREATE TYPE gp AS (amt money);
CREATE TABLE test (val gp PRIMARY KEY);

But no matter how I try to insert rows, it fails

INSERT INTO test VALUES (1); -- column "val" is of type gp but expression is of type integer
INSERT INTO test VALUES ((1)); -- column "val" is of type gp but expression is of type integer
INSERT INTO test VALUES (CAST (1 AS gp)); -- cannot cast type integer to gp
INSERT INTO test VALUES (CAST (CAST (1 AS money) AS gp)); -- cannot cast type money to gp
INSERT INTO test VALUES ((amt=1)); -- column "amt" does not exist
INSERT INTO test VALUES ((amt=1)::gp); -- column "amt" does not exist

From what I understand, the gp type should be an alias: gp::money::numeric , so why can't it cast from money to an alias of money ?

Answer 1

You should use a row constructor:

insert into test values (row(1));

Per the documentation:

The key word ROW is optional when there is more than one expression in the list.

Note, that a composite type with a single component makes a little sense. You can use a domain instead.

Answer 2

Check the below snippet

CREATE TYPE gp AS (amt money); CREATE TABLE test (val gp PRIMARY KEY); INSERT INTO test VALUES (row(1::money))

\n✓ \n\n✓ \n\n1 rows affected \n

db<>fiddle here