Postgresqlの関数

CREATE OR REPLACE FUNCTION UDF_PMT (
 InterestRate  NUMERIC(18,8),
 Nper          INTEGER,
 Pv            NUMERIC(18,4),
 Fv            NUMERIC(18,4),
 Typ           INTEGER
)
RETURNS NUMERIC(18,2)
AS $$
    SELECT round(
        CASE
        WHEN Typ = 0 THEN 
            (InterestRate / 100) /
            (Power(1 + InterestRate / 100, Nper) - 1) *
            (Pv * Power(1 + InterestRate / 100, Nper) + Fv)
        WHEN Typ = 1 THEN
            (InterestRate / 100) /
            (Power(1 + InterestRate / 100, Nper) - 1) *
            (Pv * Power(1 + InterestRate / 100, Nper) + Fv) /
            (1 + InterestRate / 100)
        END, 2)
$$ LANGUAGE SQL;