Add / REMOVE Primary Key to existing table

CREATE TABLE WITHOUT PRIMARY KEY

CREATE TABLE JSSTUDTABLE (SNO NUMERIC(10) NOT NULL)

ADD PRIMARY KEY EXISTING TABLE

ALTER TABLE JSSTUDTABLE ADD  PRIMARY KEY (SNO);

REMOVE PRIMARY KEY EXISTING TABLE 

ALTER TABLE JSSTUDTABLE DROP  constraint  PK__JSSTUDTA__CA1EE06C63D8CE75