July 2002
Beginner
424 pages
9h 30m
English
Content preview from SQL: Visual QuickStart Guide
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Understanding Constraints
Constraints allow you to define rules for values allowed in columns (Table 10.1). Your DBMS uses these rules to enforce the integrity of the database automatically. Constraints come in two flavors:
A column constraint is part of a column definition and imposes a condition on that column only.
A table constraint is declared independently of a column definition and can impose a condition on more than one column in a table. You must use a table constraint to include more than one column in a constraint.
You can specify some constraints as either column or table constraints, depending on the context in which they’re used. If a primary key contains one column, for example, you can define it as a column constraint or as a ...
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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.