Question

我想要创建的sqlite3触发器可能是也可能不是sql。涉及五个表：

Members               Groups                  GroupMembers      Accounts       
mId |name| accId      gId | name | accId      gId | mId         accId | balance

Orders
oId | accId | ammount

当有人删除某个群组时，我想为每个群组成员订阅一个群组余额的平均值。所以它应该做这样的事情：

CREATE NEW TRIGGER triggername 
BEFORE DELETE ON Groups
WHEN ((SELECT balance FROM Accounts WHERE accId=OLD.accId) = 0)
FOR EACH ROW IN 
(SELECT accId 
FROM GroupMembers JOIN Members ON GroupMembers.mId = Members.mId 
WHERE GroupMembers.gId = OLD.gId)
BEGIN
INSERT INTO Orders(accId,ammount) VALUES(accId, 
(SELECT balance FROM Accounts WHERE accId = OLD.accId)
 / 
(SELECT SUM(mId) FROM GroupMembers WHERE gId = OLD.gId)
);
END

问题是：是否可以在触发器适用的表之外的任何其他表中创建FOR EACH ROW？是否可以在FOR EACH语句之前加上WHEN语句？

Answer 1

作为documented，没有FOR EACH ROW IN ...子句这样的东西。

然而，INSERT声明can use a SELECT statement as the source of the data to be inserted。编写一个SELECT语句，为每个组成员返回一行：

CREATE TRIGGER triggername
AFTER DELETE ON Groups
FOR EACH ROW
BEGIN
    INSERT INTO Orders(accId, amount)
    SELECT accId,
           (SELECT balance
            FROM Accounts
            WHERE accId = OLD.accId) /
           (SELECT COUNT(*)
            FROM GroupMembers
            WHERE gId = OLD.gId)
    FROM Members
    WHERE mId IN (SELECT mId
                  FROM GroupMembers
                  WHERE gId = OLD.gId);
END;

（我放弃了balance = 0过滤器。）

触发器插入不同的行

1 个答案: