PostgreSQL:

CREATE TYPE

Topic

CREATE TYPE name AS
( [ attribute_name data_type [ COLLATE collation ] [, ... ] ] )

CREATE TYPE name AS ENUM
( [ 'label' [, ... ] ] )

CREATE TYPE name AS RANGE (
SUBTYPE = subtype
[ , SUBTYPE_OPCLASS = subtype_operator_class ]
[ , COLLATION = collation ]
[ , CANONICAL = canonical_function ]
[ , SUBTYPE_DIFF = subtype_diff_function ]
)

CREATE TYPE name (
INPUT = input_function,
OUTPUT = output_function
[ , RECEIVE = receive_function ]
[ , SEND = send_function ]
[ , TYPMOD_IN = type_modifier_input_function ]
[ , TYPMOD_OUT = type_modifier_output_function ]
[ , ANALYZE = analyze_function ]
[ , INTERNALLENGTH = { internallength | VARIABLE } ]
[ , PASSEDBYVALUE ]
[ , ALIGNMENT = alignment ]
[ , STORAGE = storage ]
[ , LIKE = like_type ]
[ , CATEGORY = category ]
[ , PREFERRED = preferred ]
[ , DEFAULT = default ]
[ , ELEMENT = element ]
[ , DELIMITER = delimiter ]
[ , COLLATABLE = collatable ]
)

CREATE TYPE name

Example

CREATE TYPE box;

CREATE FUNCTION my_box_in_function(cstring) RETURNS box AS ...
;
CREATE FUNCTION my_box_out_function(box) RETURNS cstring AS
... ;

CREATE TYPE box (
INTERNALLENGTH = 16,
INPUT = my_box_in_function,
OUTPUT = my_box_out_function
);

CREATE TABLE myboxes (
id integer,
description box
);