Oracle Null and Unique value

Hi Friends,

I have created a table with 2 fields such as name and rollno.
I specified rollno as unique constraint instead of not null constraint.

I have used the following query to change the unique as not null and get the following message.

Alter table student modify(rollno number(5) not null);

Table altered.

But it doesn't accept the not null concept and accepts only the unique concepts.Why? Can you just clarify my doubts?

Did u verify before Altering the table taht there are no records in table with NULL RollNumbers?

hi subhasini,


for
[I]But it doesn't accept the not null concept [/I]

sorry plz check it again it will definitly accept notnull if table alter succesfully.

for
[I]accepts only the unique concepts.Why?[/I]

see you have to drop the unique constraint on that column .

by
alter table student drop unique (rollno);

so that it will not accept contraints

hope u will get understand ..
from
sam

If the table is altered successfully ,its bound to work.