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禁用外键约束,仍然不能截断表?(SQL Server 2005)

constraints foreign-keys sql-server

larryq · 技术社区 · 15 年前

我有一个名为px_子级的表,它在px_父级上有一个外键。我想暂时禁用这个fk约束,以便截断px_父级。不过,我不确定情况如何。

我试过这些命令

ALTER TABLE PX_Child NOCHECK CONSTRAINT ALL

ALTER TABLE PX_Parent NOCHECK CONSTRAINT ALL

(truncate commands)

ALTER TABLE PX_Child CHECK CONSTRAINT ALL

ALTER TABLE PX_Parent CHECK CONSTRAINT ALL

但truncate仍然告诉我,由于外键约束,它无法截断px_父级。我环顾了整个网络,似乎找不到我做错了什么,对这个问题的基本性质感到抱歉。

4 回复 | 直到 15 年前

bobs 15 年前

如果有任何外键引用该表(包括禁用的约束),则不能截断该表。您要么需要删除外键约束,要么使用 DELETE 命令。

RJB 10 年前

有一种更简单的方法。我也面临同样的问题,找到了解决办法: https://www.mssqltips.com/sqlservertip/3347/drop-and-recreate-all-foreign-key-constraints-in-sql-server/

如果只在数据库中运行此查询,它将生成存储过程之前/之后需要包含的T-SQL,以便删除并恢复任何外键约束。

不要担心试图理解这个查询本身。

CREATE TABLE #x -- feel free to use a permanent table
(
  drop_script NVARCHAR(MAX),
  create_script NVARCHAR(MAX)
);

DECLARE @drop   NVARCHAR(MAX) = N'',
        @create NVARCHAR(MAX) = N'';

-- drop is easy, just build a simple concatenated list from sys.foreign_keys:
SELECT @drop += N'
ALTER TABLE ' + QUOTENAME(cs.name) + '.' + QUOTENAME(ct.name) 
    + ' DROP CONSTRAINT ' + QUOTENAME(fk.name) + ';'
FROM sys.foreign_keys AS fk
INNER JOIN sys.tables AS ct
  ON fk.parent_object_id = ct.[object_id]
INNER JOIN sys.schemas AS cs 
  ON ct.[schema_id] = cs.[schema_id];

INSERT #x(drop_script) SELECT @drop;

-- create is a little more complex. We need to generate the list of 
-- columns on both sides of the constraint, even though in most cases
-- there is only one column.
SELECT @create += N'
ALTER TABLE ' 
   + QUOTENAME(cs.name) + '.' + QUOTENAME(ct.name) 
   + ' ADD CONSTRAINT ' + QUOTENAME(fk.name) 
   + ' FOREIGN KEY (' + STUFF((SELECT ',' + QUOTENAME(c.name)
   -- get all the columns in the constraint table
    FROM sys.columns AS c 
    INNER JOIN sys.foreign_key_columns AS fkc 
    ON fkc.parent_column_id = c.column_id
    AND fkc.parent_object_id = c.[object_id]
    WHERE fkc.constraint_object_id = fk.[object_id]
    ORDER BY fkc.constraint_column_id 
    FOR XML PATH(N''), TYPE).value(N'.[1]', N'nvarchar(max)'), 1, 1, N'')
  + ') REFERENCES ' + QUOTENAME(rs.name) + '.' + QUOTENAME(rt.name)
  + '(' + STUFF((SELECT ',' + QUOTENAME(c.name)
   -- get all the referenced columns
    FROM sys.columns AS c 
    INNER JOIN sys.foreign_key_columns AS fkc 
    ON fkc.referenced_column_id = c.column_id
    AND fkc.referenced_object_id = c.[object_id]
    WHERE fkc.constraint_object_id = fk.[object_id]
    ORDER BY fkc.constraint_column_id 
    FOR XML PATH(N''), TYPE).value(N'.[1]', N'nvarchar(max)'), 1, 1, N'') + ');'
FROM sys.foreign_keys AS fk
INNER JOIN sys.tables AS rt -- referenced table
  ON fk.referenced_object_id = rt.[object_id]
INNER JOIN sys.schemas AS rs 
  ON rt.[schema_id] = rs.[schema_id]
INNER JOIN sys.tables AS ct -- constraint table
  ON fk.parent_object_id = ct.[object_id]
INNER JOIN sys.schemas AS cs 
  ON ct.[schema_id] = cs.[schema_id]
WHERE rt.is_ms_shipped = 0 AND ct.is_ms_shipped = 0;

UPDATE #x SET create_script = @create;

PRINT @drop;
PRINT @create;

/*
EXEC sp_executesql @drop
-- clear out data etc. here
EXEC sp_executesql @create;
*/

生成一组:

ALTER TABLE [dbo].[Whatever] DROP CONSTRAINT....
--
ALTER TABLE [dbo].[Whatever] ADD CONSTRAINT....

Paul Groke Chronial 15 年前

即使禁用了约束,SQL Server也不会允许您在约束存在时截断表。删除约束并在截断表后重新创建它。或者只需删除并重新创建表,以应用程序中更容易执行的操作为准。

BJ Coder 7 年前

当外键约束时,没有这样的选项来截断表,但是我们可以使用类似的技巧

 ALTER TABLE [dbo].[table2] DROP CONSTRAINT [FK_table2_table1]
    GO
    truncate table [table1]
GO
    ALTER TABLE [dbo].[table2]  WITH CHECK ADD  CONSTRAINT [FK_table2_table1] FOREIGN KEY([FKId])
    REFERENCES [dbo].[table1] ([ID])
    GO

    ALTER TABLE [dbo].[table2] CHECK CONSTRAINT [FK_table2_table1]
    GO