Question

我的Trigger遇到了一些麻烦。它应该是：

更新主表中插入的历史记录表并添加时间戳。
如果历史记录表中的某行已经具有相同的值，则不应添加任何内容，但应增加计数器并更新时间。
如果自上次更新以来已超过24小时，则会创建一个新行。

Sloppy pseudocode：

IF NOT EXISTS ( --if the value isn't in the history table
    SELECT History.value1 FROM History, INSERTED
    WHERE History.value1 LIKE INSERTED.value1
    AND History.value2 LIKE INSERTED.value2
       ) 
       OR EXISTS ( --or if it has been added over 24h ago
        SELECT History.value1 FROM History, INSERTED
        WHERE History.value1 LIKE INSERTED.value1
        AND History.value2 LIKE INSERTED.value2
        AND DATEDIFF(HOUR,History.time, GETDATE()) > 24
       )     
    BEGIN --Insert it
        INSERT INTO History(value1, value2, counter, time)
        SELECT value1, value2, counter GETDATE() FROM INSERTED
    END
    ELSE
    BEGIN  -- else, increase counter and add new time
        UPDATE History
        SET History.time = GETDATE(), 
                               History.Items = History.Items + INSERTED.Items
        FROM History
        JOIN INSERTED ON History.value1 = INSERTED.value1
        AND History.value2 = INSERTED.value2
            AND DATEDIFF(HOUR, _History.time, GETDATE()) < 24;
    END

示例表：

__________________________________________________
| value1 | value2 | counter | time(last updated) |
+------------------------------------------------+
| test1  | test2  |    1    |        < 24h       |
| test3  | test4  |    1    |        > 24h       |
| test3  | test4  |    1    |        < 24h       |
+------------------------------------------------+

输入：

INSERT INTO main_table(value1, value2, counter)
VALUES ('test3', 'test4', 1);

结果表：

__________________________________________________
| value1 | value2 | counter | time(last updated) |
+------------------------------------------------+
| test1  | test2  |    1    |        < 24h       |
| test3  | test4  |    1    |        > 24h       |
| test3  | test4  |    1    |        < 24h       | <--This counter+time should be updated
| test3  | test4  |    1    |        < 24h       | <--This row shouldn't be added
+------------------------------------------------+

我明白为什么会发生这种情况（因为代码发现的历史值超过24小时，无视新的一个（））但我不知道如何修复它。

Answer 1

我认为如果inserted包含行的混合，您的触发器仍会被破坏 - 因为您的IF / ELSE结构会对要采取的操作做出单一决定。

最好有MERGE，例如：

;MERGE INTO History h USING INSERTED i
   ON h.Value1 = i.Value1 and h.Value2 = i.Value2 and
      DATEDIFF(HOUR,h.time, GETDATE()) <= 24
WHEN MATCHED THEN
   UPDATE SET time = GETDATE(), Items = h.Items + i.Items
WHEN NOT MATCHED THEN
   INSERT (Value1,Value2,Items,time)
   VALUES (i.Value1,i.Value2,i.Items,GETDATE());

哪个应该替换整个触发器体。

顺便提一下，DATEDIFF计算跨越边界的过渡次数，而不是计算精确差异（例如DATEDIFF(hour,'00:59','01:01')为1）。如果你想接近24小时的截止时间，也考虑分钟和秒数，那么更好的比较是：

h.Time >= DATEADD(day,-1,GETDATE())

顺便提一下，还允许使用包含History time列的索引。

Answer 2

- 像这样更改您的标准声明。它会工作。无论如何，你写的触发器真的不好。触发器应设计为处理set not records，因为一次批量插入/更新/删除只能触发一次。

IF NOT EXISTS ( --if the value isn't in the history table
SELECT History.value1 FROM History, INSERTED
WHERE History.value1 LIKE INSERTED.value1
AND History.value2 LIKE INSERTED.value2
   ) 
   OR EXISTS ( --or if it has been added over 24h ago
    SELECT INSERTED.value1 
    FROM INSERTED
    cross apply
        (select max(History.[time]) mx_time
        from    History
        where   History.value1 LIKE INSERTED.value1
                AND History.value2 LIKE INSERTED.value2
        ) as t
    WHERE DATEDIFF(HOUR,t.mx_time, GETDATE()) >= 24
   )     
BEGIN --Insert it
    INSERT INTO History(value1, value2, items, time)
    SELECT value1, value2, items, GETDATE() FROM INSERTED
END
ELSE
BEGIN  -- else, increase counter and add new time

    UPDATE History
    SET History.time = GETDATE(), 
                           History.Items = History.Items + INSERTED.Items
    FROM History
    JOIN INSERTED ON History.value1 = INSERTED.value1
    AND History.value2 = INSERTED.value2
        AND DATEDIFF(HOUR, History.time, GETDATE()) < 24;
END

Answer 3

OMG我解决了它^^尝试修复它2个小时，当我发布到stackoverflow时我设法解决它^^

我做了什么：

更改了第二个“EXIST”测试：

OR EXISTS ( --or if it has been added over 24h ago
        SELECT History.value1 FROM History, INSERTED
        WHERE History.value1 LIKE INSERTED.value1
        AND History.value2 LIKE INSERTED.value2
        AND DATEDIFF(HOUR,History.time, GETDATE()) > 24
       )

为：

OR NOT EXISTS ( --or if it has been added over 24h ago
        SELECT History.value1 FROM History, INSERTED
        WHERE NOT History.value1 LIKE INSERTED.value1
        OR History.value2 LIKE INSERTED.value2
        OR DATEDIFF(HOUR,History.time, GETDATE()) > 24
       )

触发器无法按预期工作

3 个答案: