触发器中的Oracle to_char子查询

Question

我有一个表（会议），其中包含日期类型属性（MeetDate）和另一个varchar2类型属性（WorkWeek）。我正在尝试使用to_char函数执行After触发器以基于MeetDate值填充WorkWeek字段。分别尝试以下代码并且它们编译时没有错误，但是当我尝试插入Null for WorkWeek的行时，它给了我一个“变异触发器/函数可能看不到它”的错误。我在这做错了什么？提前感谢任何帮助。

--Code 1
Create or Replace Trigger Update_WorkWeek
After Insert On Meeting
For Each Row
Begin
Update Meeting
Set WorkWeek  = (Select to_char(:new.MeetDate, 'YYYY IW') From Dual)
Where MeetID = :new.MeetID;
End;
/
show Errors;

--Code 2
Create or Replace Trigger Update_WorkWeek
After Insert On Meeting
For Each Row
Begin
if :New.WorkWeek is Null then
Update Meeting
Set WorkWeek  = (Select to_char(:new.MeetDate, 'YYYY IW') From Dual)
Where MeetID = :new.MeetID;
End if;
End;
/
show Errors;

Answer 1

您只需要一个触发器来在插入之前更改列的值 - 并且它位于同一行，因此您不需要更新：

Create or Replace Trigger Update_WorkWeek
BEFORE Insert On Meeting
For Each Row
Begin
  :new.WorkWeek := to_char(:new.MeetDate, 'YYYY IW');
End;
/
show Errors;

如果更改了MeetDate，您可能希望该列保持最新，即：

Create or Replace Trigger Update_WorkWeek
BEFORE Insert
    OR Update OF MeetDate
On Meeting
For Each Row
Begin
  :new.WorkWeek := to_char(:new.MeetDate, 'YYYY IW');
End;
/
show Errors;