sql-server – SQL Server中的FK验证是否总是使用sys.foreign_keys中指定的索引？

2023年4月26日 204次阅读

我找不到任何讨论可以用来备份FK约束的多个可能索引的情况.

从下面的测试看来,在FK创建时FK被绑定到特定索引,这将始终用于验证FK约束,而不管以后是否添加新的更好的索引.

任何人都可以指出任何确认或否认这一点的资源吗？

CREATE TABLE T1(
    T1_Id INT IDENTITY(1,1) PRIMARY KEY CLUSTERED  NOT NULL,
    Filler CHAR(4000) NULL,
) 

INSERT INTO T1 VALUES ('');


CREATE TABLE T2(
    T2_Id INT IDENTITY(1,1) PRIMARY KEY NOT NULL,
    T1_Id INT NOT NULL CONSTRAINT FK REFERENCES T1 (T1_Id), 
    Filler CHAR(4000) NULL,
)

/*Execution Plan uses clustered index - There is no NCI*/ 
INSERT INTO T2 VALUES (1,1) 

ALTER TABLE T1 ADD CONSTRAINT
    UQ_T1 UNIQUE NONCLUSTERED(T1_Id) 

/*Execution Plan still use clustered index even after NCI created*/    
INSERT INTO T2 VALUES (1,1) 

SELECT fk.name,
       ix.name,
       ix.type_desc
FROM sys.foreign_keys fk
JOIN sys.indexes ix ON ix.object_id = fk.referenced_object_id
AND ix.index_id = fk.key_index_id
WHERE fk.name = 'FK'


ALTER TABLE T2 DROP CONSTRAINT FK
ALTER TABLE T2  WITH CHECK ADD  CONSTRAINT FK FOREIGN KEY(T1_Id)
REFERENCES T1 (T1_Id)    

/*Now Execution Plan now uses non clustered index*/    
INSERT INTO T2 VALUES (1,1)    

SELECT fk.name,
       ix.name,
       ix.type_desc
FROM sys.foreign_keys fk
JOIN sys.indexes ix ON ix.object_id = fk.referenced_object_id
AND ix.index_id = fk.key_index_id
WHERE fk.name = 'FK'

DROP TABLE T2
DROP TABLE T1

最佳答案 马丁,我道歉,这不是一个很好的答案,但既然你让我好奇,我做了一些挖掘.我可以分享的信息是：

目前的版本,包括Denali,不太可能在这种情况下考虑替代方案.

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