sql server 删除表字段和字段的约束

删除数据库表中的字段时，使用了 ：alter table 表名 drop column 列名

服务器返回的错误为：
Server: Msg 5074, Level 16, State 1, Line 1
The object 约束名 is dependent on column 列名.
Server: Msg 4922, Level 16, State 1, Line 1
ALTER TABLE DROP COLUMN 列名 failed because one or more objects access this column.

解决方法是先删除所有关于这一列的约束，然后在开始删除这一列

下面的代码为删除表 B_File 中的 Name 列。

DECLARE  @sqlCmd nvarchar(1024);
DECLARE  @tbname nvarchar(180), --要处理的表名
@fdname nvarchar(180), --要处理的字段名
@delfield bit=1  --0只删除关系,1同时删除字段

set @tbname='B_File';
set  @fdname= 'Name';

BEGIN
-- 定义游标.
DECLARE c_test_main CURSOR FAST_FORWARD FOR

--默认值约束
select sql='alter table ['+b.name+'] drop constraint ['+d.name+']'
from syscolumns a
join sysobjects b on a.id=b.id and a.name=@fdname and b.name=@tbname
join syscomments c on a.cdefault=c.id
join sysobjects d on c.id=d.id
union --外键引用
select s='alter table ['+c.name+'] drop constraint ['+b.name+']'
from sysforeignkeys a
join sysobjects b on b.id=a.constid
join sysobjects c on c.id=a.fkeyid
join syscolumns d on d.id=c.id and a.fkey=d.colid and d.name=@fdname
join sysobjects e on e.id=a.rkeyid and e.name=@tbname
join syscolumns f on f.id=e.id and a.rkey=f.colid
union --主键/唯一键/索引
select case when e.xtype in('PK','UQ') then 'alter table ['+c.name+'] drop constraint ['+e.name+']'
else 'drop index ['+c.name+'].['+a.name+']' end
from sysindexes a
join sysindexkeys b on a.id=b.id and a.indid=b.indid
join sysobjects c on b.id=c.id and c.xtype='U' and c.name=@tbname
join syscolumns d on b.id=d.id and b.colid=d.colid and d.name=@fdname
left join sysobjects e on e.id=object_id(a.name)
where a.indid not in(0,255)

-- 打开游标.
OPEN c_test_main;
--填充数据.
FETCH NEXT FROM c_test_main INTO @sqlCmd;
--假如检索到了数据，才处理.
WHILE @@fetch_status = 0
BEGIN
PRINT @sqlCmd;
exec sp_executesql @sqlcmd;--执行约束的删除操作

--填充下一条数据.
FETCH NEXT FROM c_test_main INTO @sqlCmd;
END;
-- 关闭游标
CLOSE c_test_main;
--释放游标.
DEALLOCATE c_test_main;
END;
if @delfield=1
begin

--判断表是否存在
--if exists (select 1 from sys.tables where name=@tbname and type = 'u')

--判断列是否存在
IF COL_LENGTH(@tbname, @fdname) IS not NULL
exec('alter table ['+@tbname+'] drop column ['+@fdname+']')
end