sql server 删除表字段和字段的约束

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