In Oracle, Primary key is the column which has unique values, and it cannot be null. In a table, there can be only one primary key.
CREATE TABLE table_name ( column1 datatype null/not null, column2 datatype null/not null, ... CONSTRAINT constraint_name PRIMARY KEY (column1, column2, ... column_n) );
CREATE TABLE Test2(ID Number, NAME Varchar2 CONSTRAINT test2_pk PRIMARY KEY (ID));
ALTER TABLE table_name ADD CONSTRAINT constraint_name PRIMARY KEY (column1, column2, ... column_n);
ALTER TABLE student ADD CONSTRAINT student_pk PRIMARY KEY(id);
ALTER TABLE table_name DROP CONSTRAINT constraint_name;
ALTER TABLE student DROP CONSTRAINT student_pk ;
ALTER TABLE table_name DISABLE CONSTRAINT constraint_name;
ALTER TABLE student DISABLE CONSTRAINT student_pk ;
ALTER TABLE table_name ENABLE CONSTRAINT constraint_name;
ALTER TABLE student ENABLE CONSTRAINT student_pk ;
