MySQL DatabaseLesson 55Free preview

MySQL Primary Key

This lesson is part of MySQL · All levels

Summary

A PRIMARY KEY is a column (or a combination of columns) that is the unique identity of each row in a table. The property is always UNIQUE and NOT NULL, so no two rows should have the same primary key value. The combination of AUTO_INCREMENT with the primary key makes the new line numbering automatic.

Key points

The primary key is unique and not simultaneous.
A table can only have one primary key, even if it can consist of several columns.
The primary key combines several columns called the composite primary key
Added with the Add Primary Key or live at CREATE TABLE
Primary key becomes a foreign key reference on another table

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