删除触发器不起作用，而添加触发器正常工作？答案

【问题标题】：Delete trigger doesn't work while add trigger work correctly?删除触发器不起作用，而添加触发器正常工作？
【发布时间】：2020-03-20 08:24:33
【问题描述】：

删除触发器不起作用，而添加触发器正常工作。

它应该像这样工作：“当我在 score 表中删除一条 subject_id = 1 且 score > 8 的记录时，exellentEng 将在类表中为 -1” 我不知道为什么。帮帮我

ALTER TRIGGER [dbo].[deleteExellentEnglishStudent]
ON [dbo].[dbo_score]
AFTER DELETE AS 
    BEGIN
      UPDATE x SET
        exellent_Eng -=1
      FROM dbo.dbo_class x
      JOIN dbo.dbo_student s ON s.class_id = x.class_id
      JOIN dbo.dbo_score c ON c.student_id = s.student_id
      WHERE (c.subject_id = 1 AND c.score >= 8)
      and c.score_id in (SELECT Deleted.score_id FROM Deleted)
    END

ALTER TRIGGER [dbo].[addExellentEnglishStudent] ON [dbo].[dbo_score]
    AFTER INSERT AS 
    BEGIN
      UPDATE x SET
        exellent_Eng += 1
      FROM dbo.dbo_class x
      JOIN dbo.dbo_student s ON s.class_id = x.class_id
      JOIN dbo.dbo_score c ON c.student_id = s.student_id
      WHERE (c.subject_id = 1 AND c.score >= 8)
      AND c.score_id IN
      (select Inserted.score_id from Inserted)
    END

【问题讨论】：

添加一些选择语句，例如select * from Deleted 到触发器，然后从 SSMS 中删除，这样您就可以看到结果。然后进行类似于您的更新的选择，这样您就可以看到发生了什么。

标签： sql-server tsql database-trigger

【解决方案1】：

dbo_score 表中不存在该行，因为它是一个after 触发器，因此该行已被删除。而是直接使用Deleted 伪表，例如

ALTER TRIGGER [dbo].[deleteExellentEnglishStudent]
ON [dbo].[dbo_score]
AFTER DELETE AS 
BEGIN
  UPDATE x SET
    exellent_Eng -=1
  FROM dbo.dbo_class x
  JOIN dbo.dbo_student s ON s.class_id = x.class_id
  JOIN dbo.Deleted c ON c.student_id = s.student_id
  WHERE (c.subject_id = 1 AND c.score >= 8)
END

注意：正如我在您的另一个问题上所说，如果它们每次都绝对计算值，而不是处理差异，您可能会发现编写和维护这些触发器更容易。然后您可以使用相同的逻辑进行插入、更新和删除，例如类似：

ALTER TRIGGER [dbo].[deleteExellentEnglishStudent]
ON [dbo].[dbo_score]
AFTER INSERT, UPDATE, DELETE
AS 
BEGIN
  UPDATE x SET
    exellent_Eng = (select count(*) from dbo.dbo_score where c.subject_id = 1 AND c.score >= 8)
  FROM dbo.dbo_class x
  JOIN dbo.dbo_student s ON s.class_id = x.class_id
  where S.studentid in (select student_id from Inserted union all select student_id from Deleted)
END

【讨论】：