根据Oracle PL/SQL语言参考，您需要的内容如下：

CREATE OR REPLACE TRIGGER EProd_Tariff_Add
AFTER INSERT OR UPDATE OF Date_measurement ON Elec_Prod
DECLARE
   Found_Tariff NUMBER(3)
BEGIN
   -- look up matching tariff
   SELECT ID_Tariff FROM E_tariffs
   INTO Found_Tariff 
   WHERE :NEW.Date_Measurement>=E_tariffs.Date_start
   FETCH FIRST 1  ROWS

   -- apply update
   UPDATE Elec_Prod Set ID_Tariff = Found_Tariff
END

字符串