Question

我知道这不是一种方法，但这是一个面试问题

使用触发器更新total = marks1 + marks2 + marks3。

我写了类似的东西，但是在插入语句后它没有更新。

CREATE table marks
(
marks1 int,
marks2 int,
marks3 int,
total int
)

SELECT * from marks m

insert into marks values(10,10,20,0)

drop TRIGGER total_marks
create TRIGGER total_marks ON marks
AFTER INSERT
AS
begin
SET NOCOUNT ON

DECLARE @marks1 as int
select @marks1 = inserted.marks1 FROM inserted
DECLARE @marks2 as int
select @marks1 = inserted.marks2 FROM inserted
DECLARE @marks3 as int
select @marks1 = inserted.marks3 FROM inserted
DECLARE @result as int
set @result = @marks1 + @marks2 + @marks3

update marks
set total = @result

SET NOCOUNT OFF
end

Answer 1

您的触发器不处理多行插入，将所有行更新为相同的值（而不仅仅是插入的行），并且远比必要复杂得多。你的钥匙在哪里？

CREATE TRIGGER dbo.total_marks 
 ON dbo.marks
 FOR INSERT 
AS
BEGIN
  SET NOCOUNT ON;

  UPDATE m
    SET total = i.marks1 + i.marks2 + i.marks3
    FROM dbo.marks AS m
    INNER JOIN inserted AS i
    ON m.key = i.key;
END
GO

如果你的表确实没有密钥（对我来说没有多大意义），那么你可以这样说，但它可能会更新已更新的行：

ON m.marks1 = i.marks1 AND m.marks2 = i.marks2 AND m.marks3 = i.marks3
WHERE m.total = 0;

触发更新列的总和？

1 个答案: