This example removes the primary key over column DEPTNO in table DEPARTMENT.
The constraints REPORTS_TO_EXISTS, defined on table DEPARTMENT, and WORKDEPT_EXISTS, defined on table EMPLOYEE, will be removed as well, since the primary key being removed is the parent key in those constraint relationships.
ALTER TABLE CORPDATA.EMPLOYEE DROP PRIMARY KEY
You can also remove a constraint by name, as in the following example:
ALTER TABLE CORPDATA.DEPARTMENT
DROP CONSTRAINT UNIQUE_LNAME_IN_DEPT