由于执行外键约束，无法删除索引

Question

我无法删除索引，因为某些表将它用作外键

消息 3723，级别 16，状态 6，第 1 行 允许在索引“tbl1.ix_cox”上。它被用于 FOREIGN KEY 约束执行。

我尝试在删除之前先禁用索引

ALTER INDEX ix_cox On tbl1
DISABLE
Go

但还是放不下。

我真的需要删除那些使用该索引的表上的外键吗？因为它大约有 30 张桌子。

Answer 1

如果创建索引时定义了 PRIMARY KEY 或 UNIQUE 约束 (https://docs.microsoft.com/en-us/sql/t-sql/statements/drop-index-transact-sql?view=sql-server-2017)，您将遇到同样的异常。

在这种情况下，简单的解决方案是改用 ALTER-TABLE-命令：

ALTER TABLE tbl1 DROP CONSTRAINT ix_cox

Answer 2

恐怕这是您唯一的选择。您必须删除所有引用表的外键约束，并且您不能重新创建外键约束，直到您在删除索引的表上指定另一个唯一索引。

Answer 3

早安，

这是一个完整的例子：

让我们先创建表并插入一些示例数据

use tempdb
GO

-- NOTE! 
--    This sample code presents a POOR CODING where the user
--    does not explicitly named the objects
--    or explicitly create CLUSTERED INDEX

DROP TABLE IF EXISTS dbo.Users_tbl;
DROP TABLE IF EXISTS dbo.Categories_tbl;
GO

CREATE TABLE dbo.Categories_tbl(
    CategoryID INT IDENTITY(1,1) PRIMARY KEY
    , CategoryName NVARCHAR(100)
)
GO 
-- find the CLUSTERED INDEX created automatically for us
SELECT * FROM sys.indexes
    WHERE object_id = OBJECT_ID('Categories_tbl')
GO
-- you can notice that by default the PRIMARY KEY become CLUSTERED INDEX
-- If we did not configure a different CLUSTERED INDEX
-- In my case the automatic name was: PK__Categori__19093A2BAE0EA4C3

-- Let's create the secondary table
CREATE TABLE dbo.Users_tbl(
    UserID INT IDENTITY(1,1) PRIMARY KEY
    , UserName NVARCHAR(100)
    , CategoryID INT
    , FOREIGN KEY (CategoryID) REFERENCES Categories_tbl(CategoryID)
)
GO 

-- Insert sample data
INSERT Categories_tbl (CategoryName) VALUES ('a'),('b')
GO
INSERT Users_tbl(UserName,CategoryID)
    VALUES ('a',1),('b',1)
GO

SELECT * FROM Categories_tbl
SELECT * FROM Users_tbl
GO

从主键中删除聚集索引

如果我们尝试删除 PK 的 DROP INDEX 则会收到此错误：

索引上不允许使用显式 DROP INDEX...它正在用于 PRIMARY KEY 约束强制执行。

解决方案是删除FK，删除PK，使用NONCLUSTERED索引而不是CLUSTERED创建新PK，然后创建FK

/************************************************  */
/********* REMOVE CLUSTERED INDEX from PRIMARY KEY */
/************************************************  */
------------------------------------------------------ 
-- Step 1: DROP the CONSTRAINTs
------------------------------------------------------ 
---- Get FOREIGN KEY name
SELECT DISTINCT OBJECT_NAME(f.constraint_object_id)
FROM sys.foreign_key_columns f
LEFT JOIN sys.indexes p ON p.object_id = f.referenced_object_id
    WHERE p.object_id = OBJECT_ID('Categories_tbl')
GO

-- DROP FOREIGN KEY
ALTER TABLE dbo.Users_tbl   
    DROP CONSTRAINT FK__Users_tbl__Categ__59063A47 -- Use the name we found above
GO

---- Get PRIMARY KEY name
SELECT name FROM sys.indexes
    WHERE object_id = OBJECT_ID('Categories_tbl')
GO
-- DROP PRIMARY KEY
ALTER TABLE dbo.Categories_tbl
    DROP CONSTRAINT PK__Categori__19093A2B9F118674 -- Use the name we found above
GO


------------------------------------------------------ 
-- Step 2: CREATE new CONSTRAINTs
------------------------------------------------------ 
-- And now we can create new PRIMARY KEY NONCLUSTERED
--   Since we use PRIMARY KEY We need to have index,
--   but we do not have to use CLUSTERED INDEX
--   we can have NONCLUSTERED INDEX
ALTER TABLE dbo.Categories_tbl
    ADD CONSTRAINT PK_CategoryID PRIMARY KEY NONCLUSTERED (CategoryID);
GO
-- Finaly we can create the 
ALTER TABLE dbo.Users_tbl
    ADD CONSTRAINT FK_Categories_tbl 
    FOREIGN KEY (CategoryID)     
    REFERENCES dbo.Categories_tbl(CategoryID)
GO

Answer 4

您可以暂时禁用 FK 约束 -> 删除索引 -> 重新启用约束，如

ALTER TABLE your_fk_table NOCHECK CONSTRAINT constraint_name

drop index ids_name

ALTER TABLE your_fk_table CHECK CONSTRAINT constraint_name

Answer 5

好吧，如果您在像 EzLo 这样的 30 张桌子上有一个 FK，那么进行一些自动化肯定会很好。此视图最后两列中的脚本将删除并重新添加您的 FK：

CREATE VIEW vwFK
AS
    select *, addFK = 'ALTER TABLE '+FKtable+' WITH ' + case when is_not_trusted = 1 then 'NO' else '' end + 'CHECK'
                        + ' ADD  CONSTRAINT [FK_'+FKtbl+'_'+PKtbl+'] FOREIGN KEY ('+FKcol+') '
                        + ' REFERENCES '+PKtable+' ('+PKcol+')'+' ON UPDATE '+onUpdate+' ON DELETE '+onDelete
                        + case when is_not_for_replication = 1 then ' NOT FOR REPLICATION' else '' end + ';'
                        + case when is_disabled = 1 then '  ALTER TABLE '+FKtable+' NOCHECK CONSTRAINT [FK_'+FKtbl+'_'+PKtbl+'];' else '' end
        ,dropFK = 'ALTER TABLE '+FKtable+' DROP ['+FK+'];'
    from (
        select
             PKtable    = object_schema_name(f.referenced_object_id)+'.'+object_name(f.referenced_object_id)
            ,PKtbl      = object_name(f.referenced_object_id)
            ,PKcol      = pc.name
            ,FKtable    = object_schema_name(f.parent_object_id)+'.'+object_name(f.parent_object_id)
            ,FKtbl      = object_name(f.parent_object_id)
            ,colseq     = fk.constraint_column_id
            ,FKcol      = fc.name
            ,FK         = object_name(f.object_id)
            ,onUpdate   = replace(f.update_referential_action_desc collate SQL_Latin1_General_CP1_CI_AS, '_', ' ')
            ,onDelete   = replace(f.delete_referential_action_desc collate SQL_Latin1_General_CP1_CI_AS, '_', ' ')
            ,f.is_disabled
            ,f.is_not_trusted
            ,f.is_not_for_replication
        from sys.foreign_key_columns as fk
            join sys.foreign_keys f on fk.constraint_object_id = f.object_id
            join sys.columns as fc on f.parent_object_id = fc.object_id and fk.parent_column_id = fc.column_id
            join sys.columns as pc on f.referenced_object_id = pc.object_id and fk.referenced_column_id = pc.column_id
    ) t

没有保证，但这多年来为我节省了很多的工作。 请记住在运行 dropFK 之前保存 addFK 语句！