NULL values & UNIQUE Key

[nkumarin001]

Hi,
I have some doubts regarding NULL values. Can any one help me in clearing my doubts.

I have created a table:-
create table suppliers
(
supplier_id number,
supplier_name varchar2(10)
);

Next, I will insert two records into this table.

insert into suppliers (supplier_id, supplier_name )
values ( 10565, null );

insert into suppliers (supplier_id, supplier_name )
values ( 10566, '' );

Q 1) Can any one tell which is the null value, whether it is supplier_name having 10565 or 10506.


2) Empty String is null value
or
NULL is null value

3) Because of this Null value doubts i have another doubt . How many null values can be their in a column if that column is defined as UNIQUE?


Regards,
Naveen

[debasisdas]

The supplier_id having value 10565 contains NULL in the supplier_name field.

There is no limit to the number of null values in acolumn if that column is defined as UNIQUE, simply because Null is not a value it means nothing ,it is simply null.

[prakash331]

Supplier_id=105 65 ,supplier_name is null value
Supplier_id=105 66 ,supplier_name is empty value

Null is not equal to null,empty string or blank space.
Null is nothing but unavailable.

u can use any no of null values for unique column values