SQL Server 检查约束在正确输入时失败

Question

我在表上使用检查约束来限制在表中插入的值..

这是我想要做的事情的解释

如果任何产品（轿车）与特定的 ObjLevel（丰田）相关联，则同一产品不能与另一个特定的 ObjLevel（雷克萨斯）相关联

在我对表应用检查约束后，任何包含 ObjLevel "toyota" 或 "lexus" 的插入都会失败..

create table ObjLevel(
OLID int identity,
Name varchar(50) not null
)

insert into ObjLevel values('Ford')
insert into ObjLevel values('Toyota')
insert into ObjLevel values('Lexus')
insert into ObjLevel values('GM')
insert into ObjLevel values('Infiniti')


create table ObjInstance(
OLIID int identity (20,1),
OLID int
)

insert into ObjInstance values(1)
insert into ObjInstance values(2)
insert into ObjInstance values(3)
insert into ObjInstance values(4)
insert into ObjInstance values(5)


create table Product(
PID int identity(50,1),
Name varchar(20)
)

insert into Product values ('sedan')
insert into Product values ('coupe')
insert into Product values ('hatchback')


create table ObjInstanceProd(
OLIID int,
PID int
)


create FUNCTION [dbo].[fnObjProd] (@Pid int) RETURNS bit WITH EXECUTE AS CALLER AS

BEGIN
   DECLARE @rv bit
   DECLARE @cnt int
   SET @cnt = 0
   SET @rv = 0

      SET @cnt= 
            (Select Count(*) from ObjInstanceProd olip
            join ObjInstance oli 
            on olip.OLIID = oli.OLIID
            join ObjLevel ol
            on ol.OLID = oli.OLID
            where ol.Name in ('Toyota','Lexus')
            and PID = @Pid)

            if(@cnt>0)
                SET @rv = 1

   RETURN @rv
END


ALTER TABLE [dbo].[ObjInstanceProd]  WITH CHECK ADD  CONSTRAINT [CK_OLIP] CHECK  ([dbo].[fnObjProd]([PID])=0)


--Insert Statement    
insert into ObjInstanceProd(OLIID,PID) values (22,51)

Msg 547, Level 16, State 0, Line 1
The INSERT statement conflicted with the CHECK constraint "CK_OLIP". The conflict occurred in database "tmp", table "dbo.ObjInstanceProd", column 'PID'.
The statement has been terminated.


--Execute Function    
select [dbo].[fnObjProd] (51) 
0

最初表 ObjInstanceProd 是空的。所以，无论我在表中放入什么值，只要约束中的函数返回 0，它就应该接受它。但它没有。 该函数正确返回 0（独立执行时），但由于某种原因，检查约束返回 1

Answer 1

当 CHECK 约束触发时，该行已经在表中。因此，调用了函数，由于查询返回了一行，所以函数返回1，而不是0。试试这个。删除约束，成功插入行，然后运行此查询：

SELECT OLIID, PID, dbo.fnObjProd([PID]) FROM dbo.ObjInstanceProd;

它应该为每个 PID 值返回 1。现在尝试添加约束。由于同样的原因，它会失败。

您是否考虑过为此使用触发器？如果您使用检查约束，这会将任何多行插入或更新转换为幕后的游标。根据您触摸表格的方式，这绝对会降低性能和并发性。这是一个简单的 INSTEAD OF INSERT 触发器，用于防止在单个操作中输入错误值，即使对于多行插入也是如此：

CREATE TRIGGER dbo.trObjProd 
ON dbo.ObjInstanceProd
INSTEAD OF INSERT AS
BEGIN
    SET NOCOUNT ON;

    IF NOT EXISTS
    (
      SELECT 1 FROM inserted
      WHERE EXISTS 
      (
        SELECT 1
            FROM dbo.ObjInstanceProd AS olip
            INNER JOIN dbo.ObjInstance AS oli 
            ON olip.OLIID = oli.OLIID
            INNER JOIN dbo.ObjLevel AS ol
            ON ol.OLID = oli.OLID
        WHERE 
            ol.Name in ('Toyota','Lexus')
            AND olip.PID = inserted.PID
      )
  )
  BEGIN
    INSERT ObjInstanceProd(OLIID, PID)
        SELECT OLIID, PID FROM inserted;
  END
  ELSE
  BEGIN
    RAISERROR('At least one value was not good.', 11, 1); 
    SELECT OLIID, PID FROM inserted;
  END
END
GO

如果您要坚持使用函数，这是一种更有效的方法，但是您需要定义一种方法来确定当前插入的行是否从检查中排除 - 我无法确定如何这样做是因为 dbo.ObjInstanceProd 没有任何限制。 OLIID、PID 是唯一的吗？

ALTER FUNCTION [dbo].[fnObjProd]
(
    @Pid INT
) 
RETURNS BIT
WITH EXECUTE AS CALLER 
AS
BEGIN
    RETURN 
    (
        SELECT CASE WHEN EXISTS 
        (
            SELECT 1 
                FROM dbo.ObjInstanceProd AS olip
                INNER JOIN dbo.ObjInstance AS oli 
                ON olip.OLIID = oli.OLIID
                INNER JOIN dbo.ObjLevel AS ol
                ON ol.OLID = oli.OLID
            WHERE 
                ol.Name in ('Toyota','Lexus')
                AND olip.PID = @Pid
        ) THEN 1 ELSE 0 END
    );
END
GO