我建了一个表，设置了主键[t_i_id],我现在想取消这个主键的设置，在企业管理器里不可以直接删除，我要怎么办呢？

create table [t_index]
([t_i_studentno][char](8)not null,
[t_i_name][char](20)not null,
[t_i_sex][char](2)not null,
[t_i_department][char](20)not null,
[t_i_id][char](18)not null)
on [primary]
alter table [t_index]
add constraint[pk_t_index]primary key clustered
([t_i_id])
on [primary]
go

alter table [t_index] drop constraint [pk_t_index]

on [primary]
放在
alter table [t_index]
add constraint[pk_t_index]primary key clustered
([t_i_id])
on [primary]
go
有什么意义吗？