如何编写检查以避免消息“INSERT 语句与 FOREIGN KEY 约束冲突”？

Question

我阅读并理解了以下问题中的条目：INSERT statement conflicted with the FOREIGN KEY constraint 。我明白这一点，但是，我在这种情况下，我需要将大约 1 Gb 的记录插入到表中，其中一些记录的外键冲突。查询如下所示：

IF NOT EXISTS (SELECT * FROM [dbo].[tbl_R_TaskHistory] WHERE [TaskID] = 
10000529)
BEGIN insert into [dbo].[tbl_History] 
([TaskID],[UserID],[ActD],[RequestD],[No],[SignID],[Completed]) 
values (10000529,'A0000187',NULL,5738366,0,NULL,CAST(N'2011-03-16 
04:53:37.210' AS DateTime)) END 

RequestID 上发生冲突，所以我认为必须有一种方法来进行检查以避免错误消息。 我的意思是，我希望我的查询检查 RequestID 是否没有 FOREIGN KEY 约束，它不会插入此记录并移至下一个记录。

Answer 1

如果您的查询只包含一行，您可以像这样展开检查：

IF NOT EXISTS (SELECT * FROM [dbo].[tbl_R_TaskHistory] WHERE [TaskID] = 10000529) AND EXISTS(SELECT 1 FROM [dbo].[...referencing table...] WHERE [RequestD] = 5738366)
BEGIN 
    insert into [dbo].[tbl_History] ([TaskID],[UserID],[ActD],[RequestD],[No],[SignID],[Completed]) 
    values (10000529,'A0000187',NULL,5738366,0,NULL,CAST(N'2011-03-16 04:53:37.210' AS DateTime));
END 

无论如何，如果您同时插入许多行并且出于性能考虑，最好将值存储在缓冲表中。像这样的：

insert into #tbl_History ([TaskID],[UserID],[ActD],[RequestD],[No],[SignID],[Completed]) 
values (10000529,'A0000187',NULL,5738366,0,NULL,CAST(N'2011-03-16 04:53:37.210' AS DateTime)) 
      ,(...)
      ,(...)
      ,(...)

然后，只需对引用表执行内部联接：

insert into [dbo].[tbl_History] ([TaskID],[UserID],[ActD],[RequestD],[No],[SignID],[Completed]) 
SELECT [TaskID],[UserID],[ActD],[RequestD],[No],[SignID],[Completed]
FROM #tbl_History A
INNER JOIN [dbo].[...referencing table...] B
    ON A.[RequestD] = B.[RequestD];

Answer 2

这种语法也有效

declare @a int = 5;
declare @b int = 18;

insert into sample (a, b) 
select @a, @b  
where not exists (select 1 from sample where b = @b)
  and     exists (select 1 from student where iden = @a)

---

这避免了创建#temp

insert into sample (a, b) 
select a, b 
from ( values (5,19)
            , (5,30)
            , (5,31)
            , (5,32)
            , (7,41)
            , (7,42)
     ) v(a,b)  
where not exists (select 1 from sample where b = v.b)
  and     exists (select 1 from student where iden = v.a)