是否可以向外键添加逻辑约束？

小编典典

是否可以向外键添加逻辑约束？

sql

我有两个表，并添加了外键约束。海螺-效果很好。现在，是否可以针对父表中的某些数据进一步限制这种关系？

基本上，我在父表中有动物，而对于子表，希望仅包含父数据为.... um ..哺乳动物的数据。

例如。

Animals
^^^^^^^
AnimalId INT PK NOT NULL IDENTITY
AnimalType TINYINT NOT NULL -- 1: Mammal, 2:Reptile, etc..
Name

Mammals
^^^^^^^
AnimalId INT PK FK NOT NULL
NumberOfMammaryGlads TINYINT NOT NULL

因此，我希望确保AnimalId只能是Animals.AnimalType = 1类型

这可能吗？？

我不想让某人尝试在子表中插入一些针对爬行动物的信息…

编辑：

我以为我必须使用检查约束（在下面的前两个答案中得到了确认-欢呼！），但是我不确定如何使用（例如sql语法来引用Animals表）。

更新：

亚历克斯有一个很好的帖子（如下），它对一些建议进行了基准测试……非常好的阅读！

阅读 244

2021-03-23

共1个答案

小编典典

我运行了一个小型基准测试-在这种情况下，使用UDF的方法运行速度几乎慢了100倍。

FK在CPU时间中的开销= 375 ms-297 ms = 78 ms

UDF在CPU时间中的开销= 7750毫秒-297毫秒= 7453毫秒

这是Sql代码…

-设置一个具有128K行的辅助表编号：

CREATE TABLE dbo.Numbers(n INT NOT NULL PRIMARY KEY)
GO
DECLARE @i INT;
SET @i = 1;
INSERT INTO dbo.Numbers(n) SELECT 1;
WHILE @i<128000 BEGIN
  INSERT INTO dbo.Numbers(n)
    SELECT n + @i FROM dbo.Numbers;
  SET @i = @i * 2;
END;
GO

-桌子

CREATE TABLE dbo.Animals
(AnimalId INT NOT NULL IDENTITY PRIMARY KEY,
AnimalType TINYINT NOT NULL, -- 1: Mammal, 2:Reptile, etc..
Name VARCHAR(30))
GO
ALTER TABLE dbo.Animals
ADD CONSTRAINT UNQ_Animals UNIQUE(AnimalId, AnimalType)
GO
CREATE FUNCTION dbo.GetAnimalType(@AnimalId INT)
RETURNS TINYINT
AS
BEGIN
DECLARE @ret TINYINT;
SELECT @ret = AnimalType FROM dbo.Animals
  WHERE AnimalId = @AnimalId;
RETURN @ret;
END
GO
CREATE TABLE dbo.Mammals
(AnimalId INT NOT NULL PRIMARY KEY,
SomeOtherStuff VARCHAR(10),
CONSTRAINT Chk_AnimalType_Mammal CHECK(dbo.GetAnimalType(AnimalId)=1)
);
GO

-–用UDF填充：

INSERT INTO dbo.Animals
  (AnimalType, Name)
SELECT 1, 'some name' FROM dbo.Numbers;
GO
SET STATISTICS IO ON
SET STATISTICS TIME ON
GO
INSERT INTO dbo.Mammals
(AnimalId,SomeOtherStuff)
SELECT n, 'some info' FROM dbo.Numbers;

结果是：

SQL Server parse and compile time: 
CPU time = 0 ms, elapsed time = 2 ms.
Table 'Mammals'. Scan count 0, logical reads 272135, 
    physical reads 0, read-ahead reads 0, lob logical reads 0, 
    lob physical reads 0, lob read-ahead reads 0.
Table 'Numbers'. Scan count 1, logical reads 441, physical reads 0, 
    read-ahead reads 0, lob logical reads 0, lob physical reads 0, 
    lob read-ahead reads 0.

SQL Server Execution Times:
    CPU time = 7750 ms,  elapsed time = 7830 ms.

(131072 row(s) affected)

-用FK填充：

CREATE TABLE dbo.Mammals2
(AnimalId INT NOT NULL PRIMARY KEY,
AnimalType TINYINT NOT NULL,
SomeOtherStuff VARCHAR(10),
CONSTRAINT Chk_Mammals2_AnimalType_Mammal CHECK(AnimalType=1),
CONSTRAINT FK_Mammals_Animals FOREIGN KEY(AnimalId, AnimalType)
  REFERENCES dbo.Animals(AnimalId, AnimalType)
);

INSERT INTO dbo.Mammals2
(AnimalId,AnimalType,SomeOtherStuff)
SELECT n, 1, 'some info' FROM dbo.Numbers;

结果是：

SQL Server parse and compile time: 
   CPU time = 93 ms, elapsed time = 100 ms.
Table 'Animals'. Scan count 1, logical reads 132, physical reads 0,
    read-ahead reads 0, lob logical reads 0, lob physical reads 0, 
    lob read-ahead reads 0.
Table 'Mammals2'. Scan count 0, logical reads 275381, physical reads 0,
   read-ahead reads 0, lob logical reads 0, lob physical reads 0, 
   lob read-ahead reads 0.
Table 'Numbers'. Scan count 1, logical reads 441, physical reads 0,
   read-ahead reads 0, lob logical reads 0, lob physical reads 0, 
   lob read-ahead reads 0.

SQL Server Execution Times:
   CPU time = 375 ms,  elapsed time = 383 ms.

-没有任何完整性地填充：

CREATE TABLE dbo.Mammals3
(AnimalId INT NOT NULL PRIMARY KEY,
SomeOtherStuff VARCHAR(10)
);
INSERT INTO dbo.Mammals3
(AnimalId,SomeOtherStuff)
SELECT n,  'some info' FROM dbo.Numbers;

结果是：
SQL Server解析和编译时间：CPU时间= 1毫秒，经过的时间= 1毫秒。

SQL Server Execution Times:
   CPU time = 0 ms,  elapsed time = 66 ms.
Table 'Mammals3'. Scan count 0, logical reads 272135, physical reads 0,
    read-ahead reads 0, lob logical reads 0, lob physical reads 0,
    lob read-ahead reads 0.
Table 'Numbers'. Scan count 1, logical reads 441, physical reads 0, 
    read-ahead reads 0, lob logical reads 0, lob physical reads 0, 
    lob read-ahead reads 0.

SQL Server Execution Times:
   CPU time = 297 ms,  elapsed time = 303 ms.

(131072 row(s) affected)

FK在CPU时间中的开销= 375 ms-297 ms = 78 ms
UDF在CPU时间中的开销= 7750 ms-297 ms = 7453 ms

2021-03-23