postgres time difference in minutes
CREATE OR REPLACE FUNCTION DateDiff (units VARCHAR(30), start_t TIME, end_t TIME)
RETURNS INT AS $$
DECLARE
diff_interval INTERVAL;
diff INT = 0;
BEGIN
-- Minus operator for TIME returns interval 'HH:MI:SS'
diff_interval = end_t - start_t;
diff = DATE_PART('hour', diff_interval);
IF units IN ('hh', 'hour') THEN
RETURN diff;
END IF;
diff = diff * 60 + DATE_PART('minute', diff_interval);
IF units IN ('mi', 'n', 'minute') THEN
RETURN diff;
END IF;
diff = diff * 60 + DATE_PART('second', diff_interval);
RETURN diff;
END;
$$ LANGUAGE plpgsql;