no. because if we use more than one, it leads to  
duplicate, which effects the fundamental property of unique 
key.

We can insert more than one null into table

No, we can't use more than one null value for unique key. 
Unique means it doesn't accept duplicate values.

We can insert any number of null values in the column which 
contains the unique key
the reason is NULL is not equal to anothere NUll
so each null is different so there is no question of 
duplication

If we use more than one, it leads to  
duplicate, which effects the fundamental property of unique 
key.

But......
We can insert any number of null values in the column which 
contains the unique key.
The reason is NULL is not equal to anothere NUll
so each null is different so there is no question of 
duplication

Yes,We should .That's the significance of Unique Key

If you insert data into Unique Key column it checks for the 
uniqueness of THIS NON NULL UNIQUE COLUMNAR DATA

no, because duplicate value is not allowed in unique. so 
thats why we can enter only one null value.

Unique in similar to primary key  but one difference's
primary key  duplicate records not allow and not null value
and uniquie allow one null value and duplicate records

Yes , More than one field can be NULL in a unique Key 
column. Because a Null values is not equal to another null 
value. So, no duplicate value is there.

yes,we can use more than one null value for unique key.
Bcz all null values are unique,
thing is that null is unknown ,unassignable, 
undefind ,inapplicable value and allwase null is not equal 
to null and any arithimitic operation and logical 
comparision all wase result null

no because primary key is the unique value of the table that
can not allow null&duplicate value.
so it is not possiblity use more than one null value and
duplicate valu

Yes, We can insert more the one NULL with unique key.
cos, Neither null is equal to null Nor null is not equal to
null.

No, we cannot use more than one null value in unique key.
This is the major difference between primary key and unique 
key.

Primary key cannot contain null values

Whereas unique key can contain only one null value

Yes ,we can insert more null value in a table having unique 
key,Bcoz one null vale is different frm another null value.

Fundamental principle is 2 nulls are not unique. U can 
insert N number of nulls in a unique its CONCRETE

Yes we can..
Hey guys.. don't be confused with the values and nulls. 
Unique key conforms only the values to be unique. Since the 
nulls are not any kind of value, they can occur as many 
times as they can.. nulls are nothing..

The answer to this question depends on the database that we 
are using
1. In SQL Server and DB2, we can insert only one null value 
in the Unique Key column.
2. In Oracle, we can insert multiple null values

Yes, we can use multiple Null values in case of Unique Key 
Column. This is one the main difference between Unique Key 
and Primary Key that Unique Key always allows multiple 
entries of Null Statement where as Primary Key never allows 
this.

I am hereby giving you a very very basic example which 
suggests that Unique Key can have more than one Null 
Statement :- 

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

Table created.

**********************

Now insert the values :-

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

1 row created.

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

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> commit;

Commit complete.

SQL> select * from abcd;

NAME
----------
amit
ami



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