sql - 在插入行之前验证值是否存在

Question

我有一个查询，我发送一个具有列的 TableType，EmpKey例如TaskId：

  @AssignNotificationTableType [dbo].[udf_TaskNotification] READONLY

INSERT INTO [TaskNotification] ([TaskId], [EmpKey])
    SELECT
        [ANT].[TaskId], [E].[EmpKey]
    FROM 
        @AssignNotificationTableType AS [ANT]
    INNER JOIN 
        [Employee] AS [E] ON [ANT].[EmpGuid] = [E].[EmpGuid]

所以我的表是这样的：

+--------------------------------------+--------------------------------------+--------+
|          TaskNotificationId          |                TaskId                | EmpKey |
+--------------------------------------+--------------------------------------+--------+

| EEE3D3F8-F190-E811-841F-C81F66DACA6A | D0440DEB-404C-4006-870F-E95BFFA840E0 |     44 |
| EFE3D3F8-F190-E811-841F-C81F66DACA6A | D0440DEB-404C-4006-870F-E95BFFA840E0 |     49 |
+--------------------------------------+--------------------------------------+--------+

如您所见，两个项目具有相同TaskId但不同Empkey，因此假设如果我再次发送相同TaskId D0440DEB-404C-4006-870F-E95BFFA840E0的内容，则仅当该 TaskId 中不存在 EmpKey 时才想插入行

所以如果我发送类似的东西：

+--+--------------------------------------+--------+
|  |                TaskId                | EmpKey |
+--+--------------------------------------+--------+
|  | D0440DEB-404C-4006-870F-E95BFFA840E0 |     44 |
|  | D0440DEB-404C-4006-870F-E95BFFA840E0 |     49 |
|  | D0440DEB-404C-4006-870F-E95BFFA840E0 |     54 |
+--+--------------------------------------+--------+

它只会插入最后一行，因为EmpKey 54 不存在TaskId

我尝试用 as 来做 inWHERE子句NOT IN：

INSERT INTO [TaskNotification] ([TaskId], [EmpKey])
    SELECT
        [ANT].[TaskId], [E].[EmpKey]
    FROM 
        @AssignNotificationTableType AS [ANT]
    INNER JOIN 
        [Employee] AS [E] ON [ANT].[EmpGuid] = [E].[EmpGuid]
    WHERE 
        [E].[EmpKey] NOT IN (SELECT EmpKey
                             FROM [TaskNotification]
                             WHERE TaskId = (SELECT TaskId 
                                             FROM @AssignNotificationTableType))

但是当我运行它时，它只是不插入任何东西。我究竟做错了什么？问候

Answer 1

将目标表作为左连接添加到 select 语句：

INSERT INTO [TaskNotification]
(
     [TaskId]
    , [EmpKey]
)
 SELECT
       [ANT].[TaskId]
     , [E].[EmpKey]
       FROM @AssignNotificationTableType AS [ANT]
           INNER JOIN [Employee] AS [E] ON [ANT].[EmpGuid] = [E].[EmpGuid]
           LEFT JOIN [TaskNotification] AS [TN] ON [TN].[TaskId] = [ANT].[TaskId]
               AND [TN].[EmpKey] = [E].[EmpKey]
       WHERE [TN].[PK] IS NULL -- PK stands for the primary key column 
       -- (or first column in of a multiple columns pk)

但是请注意，在多线程环境中，这样的查询可能会失败 - 有关更多信息，请阅读此 SO 帖子和它链接到的 Dan Guzman 的博客帖子。