MySQL DatabaseLesson 52Free preview

MySQL Constraints

This lesson is part of MySQL · All levels

Summary

Constraints are built-in rules of the database that restrict the type of value that can be entered into a column or table. MySQL recognizes several major constraints: primary key, foreign key, unique, not, check, and default. With constraint, data validation is done directly by the database so that data remains consistent even when input from multiple applications.

Key points

Constraint maintains data integrity by rejecting rules-breaking values
Main types: primary key, foreign key, unique, not, check, default
Constraints can be written directly at the time of creating tables or added to the ALTER tables.
If the data violates the constraint, the INSERT/UPDATE operation will be rejected by error.
The constraint naming makes it easier to manage and remove later

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