SQL Server : trigger how to read value for Insert, 更新、删除

Question

我在一个表中有触发器，并且希望在插入、更新或删除行时读取 UserId 值。怎么做？下面的代码不起作用，我在 UPDATED

上收到错误

ALTER TRIGGER [dbo].[UpdateUserCreditsLeft] 
   ON  [dbo].[Order]
   AFTER INSERT,UPDATE,DELETE
AS 
BEGIN
    -- SET NOCOUNT ON added to prevent extra result sets from
    -- interfering with SELECT statements.
    SET NOCOUNT ON;

    DECLARE 
    @UserId INT,

    SELECT @UserId = INSERTED.UserId FROM INSERTED, DELETED

    UPDATE dbo.[User] SET CreditsLeft = CreditsLeft - 1 WHERE Id = @UserId
END

Answer 1

请注意，插入、删除与插入CROSS JOIN删除含义相同，并给出每行的每种组合。我怀疑这就是你想要的。

这样的事情可能会帮助您开始......

SELECT
  CASE WHEN inserted.primaryKey IS NULL THEN 'This is a delete'
       WHEN  deleted.primaryKey IS NULL THEN 'This is an insert'
                                        ELSE 'This is an update'
  END  as Action,
  *
FROM
  inserted
FULL OUTER JOIN
  deleted
    ON inserted.primaryKey = deleted.primaryKey

根据您想要执行的操作，然后使用 inserted.userID 或 deleted.userID 等引用您感兴趣的表。

最后，请注意，inserted 和 deleted 是表，并且可以(并且确实)包含多个记录。

如果您一次插入 10 条记录，inserted 表将包含所有 10 条记录。这同样适用于删除和 deleted 表。以及更新情况下的两个表。

编辑示例 OP 编辑​​后触发。

ALTER TRIGGER [dbo].[UpdateUserCreditsLeft] 
  ON  [dbo].[Order]
  AFTER INSERT,UPDATE,DELETE
AS 
BEGIN

  -- SET NOCOUNT ON added to prevent extra result sets from
  -- interfering with SELECT statements.
  SET NOCOUNT ON;

  UPDATE
    User
  SET
    CreditsLeft = CASE WHEN inserted.UserID IS NULL THEN <new value for a  DELETE>
                       WHEN  deleted.UserID IS NULL THEN <new value for an INSERT>
                                                    ELSE <new value for an UPDATE>
                  END
  FROM
    User
  INNER JOIN
    (
      inserted
    FULL OUTER JOIN
      deleted
        ON inserted.UserID = deleted.UserID  -- This assumes UserID is the PK on UpdateUserCreditsLeft
    )
      ON User.UserID = COALESCE(inserted.UserID, deleted.UserID)

END

如果 UpdateUserCreditsLeft 的 PrimaryKey 不是 UserID，请在 FULL OUTER JOIN 中使用它。