Answer Posted / mukesh

Ques:= Can we use more than one null value for unique key?
Ans:=Yes, we can use multiple Null values in case of Unique Key
Column.

SQL> create table abcd(name varchar2(10) unique);

Table created.

SQL> insert into abcd(name)values('amit');

1 row created.

SQL> insert into abcd(name)values('MKS');

1 row created.

SQL> insert into abcd(name)values(null);

1 row created.

SQL> insert into abcd(name)values(null);

1 row created.

SQL> insert into abcd(name)values(null);

1 row created.

SQL> insert into abcd(name)values('');

1 row created.

SQL> insert into abcd(name)values('');

1 row created.

SQL> insert into abcd(name)values('');

1 row created.

SQL> select * from abcd order by name desc;

NAME
----------






amit
MKS

8 rows selected.

Note:= Here blank space above represents the entries of null
statements..!!

SQL> select nvl(name,0) from abcd;

NVL(NAME,0
----------
amit
MKS
0
0
0
0
0
0

8 rows selected.

SQL> select nvl(name,'a') from abcd;

NVL(NAME,'
----------
amit
MKS
a
a
a
a
a
a

8 rows selected.

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