Postgres 15

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DROP FUNCTION IF EXISTS polymorphic_input(arg_rec ANYCOMPATIBLE);
CREATE FUNCTION polymorphic_input(arg_rec ANYCOMPATIBLE) RETURNS TEXT
  LANGUAGE plpgsql AS
$plpgsql$
BEGIN
  IF pg_typeof(arg_rec) IN ('integer', 'numeric') THEN
    RETURN 'number';
  ELSIF pg_typeof(arg_rec)::TEXT IN ('date') THEN
    RETURN 'date';
  ELSE
    RETURN 'unknown';
  END IF;
END;
$plpgsql$;

SELECT polymorphic_input(5); -- number
SELECT polymorphic_input(date('2022-01-01')); -- date
SELECT polymorphic_input('2022-01-01'); -- unknown

DROP FUNCTION

CREATE FUNCTION

polymorphic_input

number

SELECT 1

polymorphic_input

date

SELECT 1

polymorphic_input

unknown

SELECT 1

DROP FUNCTION IF EXISTS polymorphic_input(arg_rec ANYCOMPATIBLE);
CREATE FUNCTION polymorphic_input(arg_rec ANYCOMPATIBLE) RETURNS TEXT
  LANGUAGE plpgsql AS
$plpgsql$
BEGIN
--that's a plpgsql CASE control structure
--supports multiple, comma-separated options in one case
  CASE pg_typeof(arg_rec)::text
           WHEN 'integer', 'numeric' THEN RETURN 'number';
           WHEN 'date'               THEN RETURN 'date';
          ELSE                            RETURN 'unknown';
  END CASE;
END;
$plpgsql$;

SELECT polymorphic_input(5); -- number
SELECT polymorphic_input(date('2022-01-01')); -- date
SELECT polymorphic_input('2022-01-01'); -- unknown

DROP FUNCTION

CREATE FUNCTION

polymorphic_input

number

SELECT 1

polymorphic_input

date

SELECT 1

polymorphic_input

unknown

SELECT 1

DROP FUNCTION IF EXISTS polymorphic_input(arg_rec ANYCOMPATIBLE);
CREATE FUNCTION polymorphic_input(arg_rec ANYCOMPATIBLE) RETURNS TEXT
  LANGUAGE plpgsql AS
$plpgsql$
BEGIN
--this is a plain SQL CASE conditional expression
--this form supports only one option per line
  RETURN CASE pg_typeof(arg_rec)::text
           WHEN 'integer' THEN 'number'
           WHEN 'numeric' THEN 'number'
           WHEN 'date'    THEN 'date'
           ELSE 'unknown'
  END;
END;
$plpgsql$;

SELECT polymorphic_input(5); -- number
SELECT polymorphic_input(date('2022-01-01')); -- date
SELECT polymorphic_input('2022-01-01'); -- unknown

DROP FUNCTION

CREATE FUNCTION

polymorphic_input

number

SELECT 1

polymorphic_input

date

SELECT 1

polymorphic_input

unknown

SELECT 1