women_lover_best wrote:

> When should we use allow nulls..what null signifies? If a column is
> empty say example phonenumber of a customer..it means we dont have
> customers number..so we allow null..for such a column since it is not
> required..and when I access in my app null means we dont have customers
> phone number..is this the right interpretation?

This isn't an answer. It is a supplementary question.

If the table for phone numbers had a foreign key which linked it to the
customer table then would no phone number for a customer being
represented by an absence of a phone number record completely remove the
need for a decision to use nulls.

Mike

> thks
> vishy
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