Postgres 14

By using db<>fiddle, you agree to license everything you submit by Creative Commons CC0.
CREATE TABLE test_table (col1 int, col2 varchar, col3 date, col4 date);

INSERT INTO test_table VALUES
  (1, 'foo', '2015-01-02', '2015-01-03')
, (2, 'bar', '2015-02-02', '2015-02-03')
, (3, 'baz', '2015-03-02', '2015-03-03')
;

CREATE TABLE

INSERT 0 3

-- Syntax for any Postgres version
CREATE OR REPLACE FUNCTION test_function(date, date, VARIADIC varchar[])
  RETURNS SETOF integer
  LANGUAGE sql AS
$func$
SELECT col1
FROM   test_table
WHERE  col3 > $1
AND    col4 < $2
AND    col2 = ANY($3)
$func$;

CREATE FUNCTION

SELECT * FROM test_function('2015-01-01', '2015-01-20', 'foo', 'bar', 'baz');

-- Safer with explicit type cast
SELECT * FROM test_function('2015-01-01'::date, '2015-01-20'::date, 'foo'::varchar, 'bar', 'baz');

-- Alternative form
SELECT * FROM test_function('2015-01-01', '2015-01-20', VARIADIC '{foo, bar, baz}');

test_function

1

SELECT 1

test_function

1

SELECT 1

test_function

1

SELECT 1

-- SQL-standard function body in Postgres 14+
CREATE OR REPLACE FUNCTION test_function2(date, date, VARIADIC varchar[])
  RETURNS SETOF integer
  LANGUAGE sql
BEGIN ATOMIC
SELECT col1
FROM   test_table
WHERE  col3 > $1
AND    col4 < $2
AND    col2 = ANY($3);
END;

CREATE FUNCTION

SELECT * FROM test_function2('2015-01-01', '2015-01-20', 'foo', 'bar', 'baz');

-- Safer with explicit type cast
SELECT * FROM test_function2('2015-01-01'::date, '2015-01-20'::date, 'foo'::varchar, 'bar', 'baz');

-- Alternative form
SELECT * FROM test_function2('2015-01-01', '2015-01-20', VARIADIC '{foo, bar, baz}');

test_function2

1

SELECT 1

test_function2

1

SELECT 1

test_function2

1

SELECT 1