/**
 * Creates two functions to check strings for being a time.
 * The first function checks it with the default format, the second with the
 * format given as parameter.
 */
CREATE OR REPLACE FUNCTION is_time(s VARCHAR) RETURNS BOOLEAN AS $$
BEGIN
	PERFORM s::TIME;
	RETURN TRUE;
EXCEPTION WHEN OTHERS THEN
	RETURN FALSE;
END;
$$
STRICT
LANGUAGE plpgsql IMMUTABLE
;
COMMENT ON FUNCTION is_time(s VARCHAR) IS 'Takes a varchar and checks if it is a time, uses standard date format HH24:MI:SS.US';


CREATE OR REPLACE FUNCTION is_time(s VARCHAR, f VARCHAR) RETURNS BOOLEAN AS $$
BEGIN
	PERFORM to_timestamp(s, f)::TIME;
	RETURN TRUE;
EXCEPTION WHEN OTHERS THEN
	RETURN FALSE;
END;
$$
STRICT
LANGUAGE plpgsql IMMUTABLE
;
COMMENT ON FUNCTION is_time(s VARCHAR, f VARCHAR) IS 'Takes a varchar and checks if it is a time by taking the second varchar as time format';