Ø This is used
to avoid duplicates and nulls. This will work as combination of unique and not null.
Ø Primary key
always attached to the parent table.
Ø We can add
this constraint in all three levels.
Ex:
COLUMN LEVEL
SQL> create table student12(no number(2) primary key, name
varchar(10), marks
number(3));
SQL> create table student12(no number(2) constraint pk primary key, name varchar(10),
marks number(3));
TABLE LEVEL
SQL> create table student12(no number(2) , name varchar(10), marks
number(3),
primary key(no));
SQL> create table student12(no number(2) , name varchar(10), marks
number(3),
constraint pk primary
key(no));
ALTER LEVEL
SQL> alter table student12 add primary key(no);
SQL> alter table student12 add constraint pk primary key(no);
