How to alter the primary column

[lekhrajdeshmukh]

Alter perform on primary key column please give me the query for how to alter the primary column from the table.

[susarlasireesha]

Through Alter command we can add or drop primary key
examples
ALTER TABLE emp
ADD CONSTRAINT empno_pk PRIMARY KEY (empno);
To add primary key to existing table ,we must take care that primary key column field(fields) must be not null and not duplicate.

To Drop primary key:

alter table emp
drop constraint empno_pk

[debasisdas]

To drop the primary key can also use

alter table table_name drop primary key;