Need Help "If statment condition with Master details data updated

SELECT m.RMTEST_ID,(CASE WHEN d.STD_PARAMETER <= d.GIVEN_PARAMETER THEN nvl(m.TEST_STATUS ,'A') when d.STD_PARAMETER > d.GIVEN_PARAMETER THEN nvl(m.TEST_STATUS,'R') else null END )GIVEN_PARAMETER FROM LAB_RMTEST_MST m,LAB_RMTEST_DTL d where m.RMTEST_ID=d.RMTEST_ID and m.RMTEST_ID=:P21_RMTEST_ID