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