Oracle:在触发器中使用子查询 [英] Oracle: Using subquery in a trigger

问题描述

如何解决Oracle不允许在触发器中使用子查询的限制.

How can I work around the Oracle's limitation of not allowing subqueries in triggers.

这是我尝试创建的示例触发器，但由于无法使用子查询而无法创建.

Here's an example trigger I'm trying to create, but am unable to because I can't use a subquery.

CREATE OR REPLACE TRIGGER trigger_w_subquery
AFTER UPDATE OR INSERT ON project_archiving
FOR EACH ROW WHEN (old.archiving_status <> new.archiving_status
  AND new.archiving_status = 1
  AND (SELECT offer FROM projects WHERE projnum = :new.projnum) IS NULL
)
BEGIN
  INSERT INTO offer_log (offer, status, date)
  VALUES (null, 9, sysdate);
END;

推荐答案

此触发器可以做到:

CREATE OR REPLACE TRIGGER trigger_w_subquery
AFTER UPDATE OR INSERT ON project_archiving
FOR EACH ROW WHEN (old.archiving_status <> new.archiving_status
  AND new.archiving_status = 1
)
DECLARE
  l_offer projects.offer%TYPE;
BEGIN
  SELECT offer INTO l_offer 
  FROM projects 
  WHERE projnum = :new.projnum;

  IF l_offer IS NULL THEN
    INSERT INTO offer_log (offer, status, date)
    VALUES (null, 9, sysdate);
  END IF;
END;

我假设从项目中进行选择将始终找到一行；如果不是这样，它将引发您可能需要处理的NO_DATA_FOUND异常.

I have assumed that the select from projects will always find a row; if not it will raise a NO_DATA_FOUND exception that you may need to handle.

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