sql - 如何删除所有表中的所有外键约束？

Question

我想编写sql命令来删除所有表中的所有约束。我在网上搜索了一下，发现如果数据库较小且不复杂，以下内容可以正常工作。

DECLARE @name VARCHAR(128) 
DECLARE @constraint VARCHAR(254) 
DECLARE @SQL VARCHAR(254) 
DECLARE @schema VARCHAR(128)

SELECT @name = (SELECT TOP 1 TABLE_NAME FROM INFORMATION_SCHEMA.TABLE_CONSTRAINTS WHERE constraint_catalog=DB_NAME() AND CONSTRAINT_TYPE = 'FOREIGN KEY' ORDER BY TABLE_NAME) 
SELECT @schema = (SELECT TOP 1 schema_name(schema_id) FROM sys.objects WHERE [name] = @name) 

WHILE @name is not null 
BEGIN 
    SELECT @constraint = (SELECT TOP 1 CONSTRAINT_NAME FROM INFORMATION_SCHEMA.TABLE_CONSTRAINTS WHERE constraint_catalog=DB_NAME() AND CONSTRAINT_TYPE = 'FOREIGN KEY' AND TABLE_NAME = @name ORDER BY CONSTRAINT_NAME) 
    WHILE @constraint IS NOT NULL 
    BEGIN 
        SELECT @SQL = 'ALTER TABLE ' + @schema + '.[' + RTRIM(@name) +'] DROP CONSTRAINT [' + RTRIM(@constraint) +']' 
        EXEC (@SQL) 
        PRINT 'Dropped FK Constraint: ' + @constraint + ' on ' + @name 
        SELECT @constraint = (SELECT TOP 1 CONSTRAINT_NAME FROM INFORMATION_SCHEMA.TABLE_CONSTRAINTS WHERE constraint_catalog=DB_NAME() AND CONSTRAINT_TYPE = 'FOREIGN KEY' AND CONSTRAINT_NAME <> @constraint AND TABLE_NAME = @name ORDER BY CONSTRAINT_NAME) 
    END 
SELECT @name = (SELECT TOP 1 TABLE_NAME FROM INFORMATION_SCHEMA.TABLE_CONSTRAINTS WHERE constraint_catalog=DB_NAME() AND CONSTRAINT_TYPE = 'FOREIGN KEY' ORDER BY TABLE_NAME) 
SELECT @schema = (SELECT TOP 1 schema_name(schema_id) FROM sys.objects WHERE [name] = @name) 
END 
GO 

如果我使用更复杂的数据库甚至 AdventureWork 运行它，它就不起作用。它显示了一些如下错误。

Msg 3728, Level 16, State 1, Line 1
'FK_ap_invoice_modification_type_id' is not a constraint.
Msg 3727, Level 16, State 0, Line 1
Could not drop constraint. See previous errors.
Msg 3725, Level 16, State 0, Line 1
The constraint 'PK_ap_invoice' is being referenced by table '_drop_now_ap_invoice_detail', foreign key constraint 'FK_ap_invoice_detail_ap_invoice'.
Msg 3727, Level 16, State 0, Line 1
Could not drop constraint. See previous errors.

原因是一些FK被其他表引用了。我必须运行这个脚本几次，直到数据库干净为止。

我想知道如何清除数据库中的所有FK。

Answer 1

周围有很多关于该主题的信息。检查this detailed answer作者:@AaronBertrand。它讨论了暂时禁用外键，但是阅读全部内容并随意修改，您将有一个很好的脚本可以使用并取得很多成果。

从我这边来看，我可以提出 2 个不同的脚本来获取所有外键。在这两种情况下，取消注释 --EXEC (@SQL) 以执行 ALTER 代码。或者您可以等到它打印出所有的 alter 子句，然后复制粘贴来执行它们。

第一个使用 INFORMATION_SCHEMA 来获取约束:

DECLARE @SQL VARCHAR(MAX)=''
SELECT @SQL = @SQL + 'ALTER TABLE ' + QUOTENAME(FK.TABLE_SCHEMA) + '.' + QUOTENAME(FK.TABLE_NAME) + ' DROP CONSTRAINT [' + RTRIM(C.CONSTRAINT_NAME) +'];' + CHAR(13)
--SELECT K_Table = FK.TABLE_NAME, FK_Column = CU.COLUMN_NAME, PK_Table = PK.TABLE_NAME, PK_Column = PT.COLUMN_NAME, Constraint_Name = C.CONSTRAINT_NAME
  FROM INFORMATION_SCHEMA.REFERENTIAL_CONSTRAINTS C
 INNER JOIN INFORMATION_SCHEMA.TABLE_CONSTRAINTS FK
    ON C.CONSTRAINT_NAME = FK.CONSTRAINT_NAME
 INNER JOIN INFORMATION_SCHEMA.TABLE_CONSTRAINTS PK
    ON C.UNIQUE_CONSTRAINT_NAME = PK.CONSTRAINT_NAME
 INNER JOIN INFORMATION_SCHEMA.KEY_COLUMN_USAGE CU
    ON C.CONSTRAINT_NAME = CU.CONSTRAINT_NAME
 INNER JOIN (
            SELECT i1.TABLE_NAME, i2.COLUMN_NAME
              FROM INFORMATION_SCHEMA.TABLE_CONSTRAINTS i1
             INNER JOIN INFORMATION_SCHEMA.KEY_COLUMN_USAGE i2
                ON i1.CONSTRAINT_NAME = i2.CONSTRAINT_NAME
            WHERE i1.CONSTRAINT_TYPE = 'PRIMARY KEY'
           ) PT
    ON PT.TABLE_NAME = PK.TABLE_NAME

--EXEC (@SQL)

PRINT @SQL

这个使用不同的系统 View 和 CTE 表。

DECLARE @SQL varchar(4000)=''
;WITH ReferencingFK AS 
(
    SELECT fk.Name AS 'FKName', OBJECT_NAME(fk.parent_object_id) 'ParentTable',
            cpa.name 'ParentColumnName', OBJECT_NAME(fk.referenced_object_id) 'ReferencedTable',
            cref.name 'ReferencedColumnName'
    FROM sys.foreign_keys fk
    INNER JOIN sys.foreign_key_columns fkc ON fkc.constraint_object_id = fk.object_id
    INNER JOIN sys.columns cpa ON fkc.parent_object_id = cpa.object_id AND fkc.parent_column_id = cpa.column_id
    INNER JOIN sys.columns cref ON fkc.referenced_object_id = cref.object_id AND fkc.referenced_column_id = cref.column_id
)
SELECT @SQL = @SQL + 'ALTER TABLE ' + ParentTable + ' DROP CONSTRAINT [' + RTRIM(FKName) +'];' + CHAR(13)
--SELECT FKName, ParentTable, ParentColumnName, ReferencedTable, ReferencedColumnName
  FROM ReferencingFK
 WHERE ReferencedTable = 'Employee'
 ORDER BY ParentTable, ReferencedTable, FKName

--EXEC (@SQL) 

PRINT @SQL