带有约束的SQL Server 2005 drop column

我有一个带有"DEFAULT"约束的列.我想创建一个删除该列的脚本.

问题是它返回此错误:

Msg 5074, Level 16, State 1, Line 1  
The object 'DF__PeriodSce__IsClo__4BCC3ABA' is dependent on column 'IsClosed'. 
Msg 4922, Level 16, State 9, Line 1 
ALTER TABLE DROP COLUMN IsClosed failed because one or more objects access this column.

我找不到一种简单的方法来删除一个列及其所有相关的约束(只发现了查看系统表的大脚本......必须(!!)这是一个"好"的方法.)

由于DEFAULT约束的名称是随机生成的,我不能按名称删除它.

更新:
约束类型为"DEFAULT".

我看到了你们提出的解决方案,但我发现它们都非常"脏"......你不觉得吗？我不知道它是用于Oracle还是MySQL,但它可以做类似的事情:

DROP COLUMN xxx CASCADE CONSTRAINTS 

它会丢弃所有相关的约束......或者至少它会自动删除映射到该列的约束(至少CHECK约束!)

在MSSQL中没有类似的东西吗？

这是一个脚本,它将删除列及其默认约束.替换MYTABLENAME并MYCOLUMNNAME适当.

declare @constraint_name sysname, @sql nvarchar(max)

select @constraint_name = name 
from sys.default_constraints 
where parent_object_id = object_id('MYTABLENAME')
AND type = 'D'
AND parent_column_id = (
    select column_id 
    from sys.columns 
    where object_id = object_id('MYTABLENAME')
    and name = 'MYCOLUMNNAME'
    )

set @sql = N'alter table MYTABLENAME drop constraint ' + @constraint_name
exec sp_executesql @sql

alter table MYTABLENAME drop column MYCOLUMNNAME

go

此查询查找给定表的默认约束.它不是很好,我同意:

select 
    col.name, 
    col.column_id, 
    col.default_object_id, 
    OBJECTPROPERTY(col.default_object_id, N'IsDefaultCnst') as is_defcnst, 
    dobj.name as def_name
from sys.columns col 
    left outer join sys.objects dobj 
        on dobj.object_id = col.default_object_id and dobj.type = 'D' 
where col.object_id = object_id(N'dbo.test') 
and dobj.name is not null

[编辑]根据Julien N的评论更新

也许它可以帮助更多:

declare @tablename nvarchar(200)
declare @colname nvarchar(200)
declare @default sysname, @sql nvarchar(max)

set @tablename = 'your table'
set @colname = 'column to drop'

select @default = name 
from sys.default_constraints 
where parent_object_id = object_id(@tablename)
AND type = 'D'
AND parent_column_id = (
    select column_id 
    from sys.columns 
    where object_id = object_id(@tablename)
    and name = @colname 
    )

set @sql = N'alter table ' + @tablename + ' drop constraint ' + @default
exec sp_executesql @sql

set @sql = N'alter table ' + @tablename + ' drop column ' + @colname
exec sp_executesql @sql

只需要设置@tablename和@colname变量来删除列.

> select CONSTRAINT_NAME from INFORMATION_SCHEMA.CONSTRAINT_COLUMN_USAGE
> WHERE TABLE_NAME = '' AND COLUMN_NAME = 'IsClosed'

这不是正确的解决方案,因为它在这里解释:http://msdn.microsoft.com/en-us/library/aa175912.aspx:

遗憾的是,列默认约束的名称未保留在ANSI COLUMNS视图中,因此您必须返回系统表才能找到名称

我发现获取DEFAULT约束名称的唯一方法是此请求:

select  
    t_obj.name              as TABLE_NAME
    ,c_obj.name             as CONSTRAINT_NAME
    ,col.name               as COLUMN_NAME

from    sysobjects  c_obj
join    sysobjects  t_obj on c_obj.parent_obj = t_obj.id  
join    sysconstraints con on c_obj.id  = con.constid
join    syscolumns  col on t_obj.id = col.id
            and con.colid = col.colid
where
    c_obj.xtype = 'D'

我是唯一一个发现它的疯狂是不能轻易删除的约束,只有涉及我试图删除列？
我需要执行一个带有3个连接的请求才能获得名称...

我也认为在SQL服务器中没有可用的级联丢包是一个缺点.我通过查询系统表来解决这个问题,方法与此处描述的其他人一样:

INFORMATION_SCHEMA.CONSTRAINT_COLUMN_USAGE仅列出外键,主键和唯一约束.

查找默认约束的唯一方法是在sys.default_constraints中查找它们.

这里还没有提到的是,索引也会导致删除列失败,因此您还需要删除使用列的所有索引,然后才能继续删除列.

生成的脚本不漂亮,但我将它放在存储过程中以便能够重用它:

CREATE PROCEDURE DropColumnCascading @tablename nvarchar(500), @columnname nvarchar(500)
AS

SELECT CONSTRAINT_NAME, 'C' AS type
INTO #dependencies
FROM INFORMATION_SCHEMA.CONSTRAINT_COLUMN_USAGE WHERE TABLE_NAME = @tablename AND COLUMN_NAME = @columnname

INSERT INTO #dependencies
select d.name, 'C'
from sys.default_constraints d
join sys.columns c ON c.column_id = d.parent_column_id AND c.object_id = d.parent_object_id
join sys.objects o ON o.object_id = d.parent_object_id
WHERE o.name = @tablename AND c.name = @columnname

INSERT INTO #dependencies
SELECT i.name, 'I'
FROM sys.indexes i
JOIN sys.index_columns ic ON ic.index_id = i.index_id and ic.object_id=i.object_id
JOIN sys.columns c ON c.column_id = ic.column_id and c.object_id=i.object_id
JOIN sys.objects o ON o.object_id = i.object_id
where o.name = @tableName AND i.type=2 AND c.name = @columnname AND is_unique_constraint = 0

DECLARE @dep_name nvarchar(500)
DECLARE @type nchar(1)

DECLARE dep_cursor CURSOR
FOR SELECT * FROM #dependencies

OPEN dep_cursor

FETCH NEXT FROM dep_cursor 
INTO @dep_name, @type;

DECLARE @sql nvarchar(max)

WHILE @@FETCH_STATUS = 0
BEGIN
    SET @sql = 
        CASE @type
            WHEN 'C' THEN 'ALTER TABLE [' + @tablename + '] DROP CONSTRAINT [' + @dep_name + ']'
            WHEN 'I' THEN 'DROP INDEX [' + @dep_name + '] ON dbo.[' + @tablename + ']'
        END
    print @sql
    EXEC sp_executesql @sql
    FETCH NEXT FROM dep_cursor 
    INTO @dep_name, @type;
END

DEALLOCATE dep_cursor

DROP TABLE #dependencies

SET @sql = 'ALTER TABLE [' + @tablename + '] DROP COLUMN [' + @columnname + ']'

print @sql
EXEC sp_executesql @sql