How to use check constraints in mysql

The CHECK constraint in MySQL is used to limit the range of data values ​​in the table, using the syntax: ALTER TABLE table_name ADD CONSTRAINT constraint_name CHECK (column_name expression). Advantages include data integrity, performance, and maintainability. Notes are that it only applies to a single column, the expression must return a Boolean value, and the constraint name must be unique.

CHECK constraints in MySQL

In MySQL, CHECK constraints are used to limit the data values ​​in a table. It defines the range of values ​​allowed to be stored in the table by specifying a Boolean expression.

How to use CHECK constraints

To create a CHECK constraint, use the following syntax:

<code class="sql">ALTER TABLE table_name ADD CONSTRAINT constraint_name CHECK (column_name expression);</code>

Where:

• table_name is the name of the table to which constraints are to be added.
• constraint_name is the unique name of the constraint.
• column_name is the name of the column to which the constraint is to be applied.
• expression is a Boolean expression that defines the values ​​allowed to be stored in the column.

How to use CHECK constraint example

For example, you want to create a table named employees that only allows positive numbers. ##salary column, you can use the following constraints:

<code class="sql">ALTER TABLE employees ADD CONSTRAINT positive_salary CHECK (salary > 0);</code>

Advantages of CHECK constraints

Using CHECK constraints has the following advantages:

• Data integrity: It ensures that only values ​​that meet the constraints can be inserted into the table.
• Performance: It can quickly validate data when inserting, thereby reducing the storage of invalid data.
• Maintainability: It makes column constraints easier to understand and manage.

Notes on CHECK constraints

The following need to be noted:

CHECK constraints can only be applied to a single column.
• Expressions must always return a TRUE or FALSE value.
• The constraint name must be unique in the table.

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