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Primary keys - the basics
Single-column primary keys
12. ...but one there should be!
Multicolumn primary keys
Auto-increment columns and sequences
Revision

Instruction

Good. As you can see, it's impossible to create a table with two or more primary keys. There are other ways to make two columns unique. You'll get to know them in the next part of the course.

Is it possible to create a table without a primary key? Of course it is. Up to this point, we've only created tables without primary keys because we had not known they existed. It is, however, advisable to have a primary key in each table. From now on, let's keep to that rule.

Exercise

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