CASE 语句不执行任何操作

Question

我有一个带有 case 语句的触发器。在 ELSE 块中代码的最后一部分中，我希望触发器不执行任何操作并在前面的 CASE 语句中的值不匹配时退出。我该怎么做呢：

create or replace TRIGGER  "CONVEYANCE_REQUEST_T3"  
BEFORE  
insert or update on "CONVEYANCE_REQUEST"  
for each row  
begin  

CASE   
 when :NEW.REGULAR_TRAVEL_MODE = '2 WHEELER' THEN  
 BEGIN  
     CASE  
         when :NEW.WAY_TYPE = 'ONE WAY' THEN   
              SELECT RATE_PER_KM * (SELECT DISTANCE_ONEWAY  FROM     DISTANCE_MASTER WHERE PROJECT_CODE = :NEW.PROJECT_CODE ) * 1 INTO     :NEW.REGULAR_AMOUNT FROM CONVEYANCE_RATE WHERE TRAVEL_MODE = :NEW.REGULAR_TRAVEL_MODE;  
         WHEN :NEW.WAY_TYPE ='TWO WAY' THEN  
              SELECT RATE_PER_KM * (SELECT DISTANCE_ONEWAY FROM DISTANCE_MASTER WHERE PROJECT_CODE = :NEW.PROJECT_CODE ) * 2 INTO :NEW.REGULAR_AMOUNT FROM CONVEYANCE_RATE WHERE TRAVEL_MODE = :NEW.REGULAR_TRAVEL_MODE;  
     END CASE;  
 END;  
 when :NEW.REGULAR_TRAVEL_MODE = '4 WHEELER' THEN  
 BEGIN  
     CASE  
        when :NEW.WAY_TYPE = 'ONE WAY' THEN   
              SELECT RATE_PER_KM * (SELECT DISTANCE_ONEWAY   FROM DISTANCE_MASTER WHERE PROJECT_CODE = :NEW.PROJECT_CODE ) * 1 INTO :NEW.REGULAR_AMOUNT FROM CONVEYANCE_RATE WHERE TRAVEL_MODE = :NEW.REGULAR_TRAVEL_MODE;  
         WHEN :NEW.WAY_TYPE ='TWO WAY' THEN  
              SELECT RATE_PER_KM * (SELECT DISTANCE_ONEWAY  FROM DISTANCE_MASTER WHERE PROJECT_CODE = :NEW.PROJECT_CODE ) * 2 INTO :NEW.REGULAR_AMOUNT FROM CONVEYANCE_RATE WHERE TRAVEL_MODE = :NEW.REGULAR_TRAVEL_MODE;  
     END CASE;  
 END;
 ELSE 
  ****statement to just exit & not do anything*****

 END CASE;  
END;  

Answer 1

这是一个非常复杂的 case 语句，每次都重复本质上相同类型的 select 语句。

由于每个语句之间的唯一区别在于乘数是 1 还是 2，因此您可以在一个包含带有 case 表达式的 sql 语句的 case 语句中重写整个内容，如下所示：

create or replace trigger  "CONVEYANCE_REQUEST_T3"  
before  
insert or update on "CONVEYANCE_REQUEST"  
for each row  
begin  
  case when rate_per_km in ('2 WHEELER', '4 WHEELER')
            and new.way_type in ('ONE WAY', 'TWO WAY') then
            select rate_per_km
                     * (select distance_oneway from distance_master where project_code = :new.project_code)
                     * case when :new.way_type = 'ONE WAY'
                                 then 1
                            when :new.way_type = 'TWO WAY'
                                 then 2
                            else null
                     end regular_amount
            into   :new.regular_amount
            from   conveyance_rate where travel_mode = :new.regular_travel_mode;
       else null;
  end case; 
end;
/

您甚至可以摆脱没有外部 case 语句的情况（尽管您必须将条件推rate_per_km in ('2 WHEELER', '4 WHEELER')入 case 表达式中，但是每次都必须为每一行运行查询，如果您的大部分插入的行不是两轮或四轮车。