Comments on: Null – again

By: Jared

Jared — Fri, 07 Sep 2012 19:24:04 +0000

Thanks for your comment Jonathan. I considered that as well, but thought my question might bring some clarity to folks that may be reading this and have only recently started learning about oracle. The astute newbies will create and test the table with the various methods. :)

By: Jonathan Lewis

Jonathan Lewis — Fri, 07 Sep 2012 19:07:09 +0000

Jared,

I nearly asked a similar question – then realised that I hadn’t made any explicit comment to the effect that comparisons with null should be “is NULL” rather than “= NULL”, so I suspect that Sasa’s comment was intended to make that point for me (even though it’s redundant in the example).

By: Jared

Jared — Fri, 07 Sep 2012 14:47:22 +0000

Sasa, what is the purpose of including ‘is null’ in the constraint?

By: Sasa Petkovic

Sasa Petkovic — Fri, 07 Sep 2012 07:55:06 +0000

create table t1 (
	v1 varchar2(10),
	constraint c1 check (v1 = 'A' or v1 is null)
);

With this insert into t1 values(‘B’); would be prevented…

By: Jared

Jared — Thu, 06 Sep 2012 18:02:26 +0000

This is one of those logic bugs that I might look at several times and not notice the error.
Of course it is not necessary to include the check for null in the constraint anyway, just keep the column nullable.