CREATE FUNCTION SALES_TAX(IN sales real,OUT tax real) AS $$ BEGIN tax := sales * 0.2; END; $$ LANGUAGE plpgsql; CREATE OR REPLACE FUNCTION SALES_TAX2(IN sales real) RETURNS real AS $$ BEGIN RETURN sales * 0.2; END; $$ LANGUAGE plpgsql; CREATE OR REPLACE FUNCTION SALES_TAX3(INOUT sales real) $$ BEGIN sales = sales * 0.2; END; $$ LANGUAGE plpgsql;