July 2005
Intermediate to advanced
1032 pages
27h 10m
English
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NULL Values
NULL values represent missing, unknown, or not-applicable values. For example, let's say that you want to add a membership_expiration_date to the customers table. Some customers might be permanent members—their memberships will never expire. For those customers, the membership_expiration_date is not applicable and should be set to NULL. You may also find some customers who don't want to provide you with their birth dates. The birth_date column for these customers should be NULL.
In one case, NULL means not applicable. In the other case, NULL means don't know. A NULL membership_expiration_date does not mean that you don't know the expiration date, it means that the expiration date does not apply. A NULL birth_date does not mean that ...
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.