Question

我有一个带有case语句的触发器。在ELSE块的代码的最后一部分中，我希望触发器不执行任何操作，如果值在先前的CASE语句中不匹配则退出。我该怎么做：

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案例陈述，每次重复基本上相同的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，所以你可以在一个包含带有case表达式的sql语句的case语句中重写整个事物：

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;
/

你甚至可以不使用外部case语句（尽管你必须将rate_per_km in ('2 WHEELER', '4 WHEELER')条件推送到case表达式中，但是每次对每行都必须运行查询如果插入的大多数行不是2或4轮车，可能会降低性能。

CASE声明什么都不做

1 个答案: