How can I use the SQL to create a primary key for a existing table?

Question

create table a(bm number,mc varchar2(20));
when the table was created,i want to make the column bm as
the primary key and my SQL is "alter table a enable primary key bm",the system show
me error,how can I write the right one?

Answer 1

create table a(bm number,mc varchar2(20));
when the table was created,i want to make the column bm as
the primary key and my SQL is "alter table a enable primary key bm",the system show
me error,how can I write the right one? You do not have any primary key defined on your table yet, so, it does not make sense to enable it (if at all possible) !
You need to add PRIMARY KEY using something like this:
SQL> alter table a add constraint pk_a_bm primary key (bm) ;