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Question

變量如何聲明temp變量，雖然我根據我已經學習語法，而且，它是正確的，但後來太，它顯示錯誤：Undefined temp and t.

CREATE TRIGGER check_reciever BEFORE INSERT 
ON one_to_one FOR each row 
BEGIN 
select employee_id into temp from employee_master where employee_id = NEW.reciever_id; 
IF temp!=0 THEN 
insert into one_to_one values(new.message_id,new.reciever_id,new.read); 
ELSE 
    select count(*) into t from parent_master where parent_id=new.reciever_id; 
    IF t!=0 THEN 
    insert into one_to_one values(new.message_id,new.reciever_id,new.read); 
    END IF; 
END IF; 
END 

Answer 1

你錯過了其被用於聲明變量（如可從它的名字被猜到）的DECLARE子句：

CREATE TRIGGER check_reciever BEFORE INSERT 
ON one_to_one FOR each row 
-- Begining of the DECLARE section you're missing 
DECLARE 
    temp NUMBER; 
    t NUMBER; 
-- End of the missing section 
BEGIN 
    select employee_id into temp from employee_master where employee_id = NEW.reciever_id; 
    IF temp!=0 THEN 
     insert into one_to_one values(new.message_id,new.reciever_id,new.read); 
    ELSE 
     select count(*) into t from parent_master where parent_id=new.reciever_id; 
     IF t!=0 THEN 
      insert into one_to_one values(new.message_id,new.reciever_id,new.read); 
     END IF; 
    END IF; 
END 

EDIT：以上是Oracle解決方案，因爲每OP的標籤。對於MySQL，該DECLARE語法稍有不同：

CREATE TRIGGER check_reciever BEFORE INSERT 
ON one_to_one FOR each row 
BEGIN 
    -- Declarations 
    DECLARE temp NUMERIC; 
    DECLARE t NUMERIC; 
    -- End declarations 
    select employee_id into temp from employee_master where employee_id = NEW.reciever_id; 
    IF temp!=0 THEN 
     insert into one_to_one values(new.message_id,new.reciever_id,new.read); 
    ELSE 
     select count(*) into t from parent_master where parent_id=new.reciever_id; 
     IF t!=0 THEN 
      insert into one_to_one values(new.message_id,new.reciever_id,new.read); 
     END IF; 
    END IF; 
END