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From Ravinder Reddy Pandiri <pand...@students.iiit.ac.in>
Subject Re: regarding unique keys in derby..
Date Mon, 23 Jul 2007 21:40:08 GMT
On Fri, 20 Jul 2007, Kathey Marsden wrote:

> Ravinder Reddy wrote:
>>
>>     hi all,
>>         w.r.t DERBY-2945(convert lang/primarykey.sql to junit)
>> I have a small doubt.
>> 
>> There is a test for verifying a unique key can not contain nulls.
>> 
>> 1)-- verify that a unique key can not contain nulls
>>   create table pos1 (c1 int not null unique, c2 int);
>>   insert into pos1 (c1) values(null);
>>   insert into pos1 (c1) values(null);
>>   select * from pos1;
>>   drop table pos1;
>>     And It tests that null values are not allowed in c1.
>>     Irrespective of uniqueness , c1 can't contain null values as it is 
>> defined as not null.It seems that the test is wrong.
> The test seems reasonable enough, but I guess it is really testing that 
> not null works #:)
> We could have a test like the one below if we don't have one already.
> ij> create table pos1 (c1 int unique, c2 int);
> ERROR 42831: 'C1' cannot be a column of a primary key or unique key 
> because it can contain null values.
>> 
>> 2) I am shocked to know that Derby doesn't allow a unique key column to 
>> contain NULL values.can some somebody justify it.?
>> 
> You are easily shocked #:)
 	I think most of the database systems(oracle , db2 , mySql , 
postgreSQL et al) allow a unique key column to contain NULL values.
That's why I am shocked..!!!!!

Thank You.
>
>
> Kathey
>
>
>
>

-- 
******************************************************************************

    Every problem that has been solved can be solved again in a better way

                                                   - Ravinder Reddy

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