How many types of constraints are there in mysql?

MySQL provides 10 types of constraints: primary key constraints, foreign key constraints, unique key constraints, non-null constraints, check constraints, default value constraints, auto-increment constraints, cascade constraints, index constraints and space constraints. Use To ensure data consistency, integrity and validity.

Constraint types in MySQL

MySQL supports the following types of constraints:

1. Primary key constraints

• # uniquely identify each row in the table.
• Must be a non-NULL value.

2. Foreign key constraints

• reference a column in another table to establish a relationship between tables.
• Ensure data consistency and integrity.

3. Unique key constraints

• Ensure that the combined values ​​of the specified columns in each row in the table are unique.
• Allow NULL values.

4. Non-null constraint

• prohibits null values ​​for specified columns in the table.

5. Check constraints

• Apply an expression to a column to verify that its value meets specific conditions.
• Contributes to data validation and data integrity.

6. Default value constraint

• Specifies a default value for the column, which is used when no value is specified when inserting a new row.

7. Auto-increment constraint

• Specify an auto-increment value for the column, usually used for primary key or ID columns.

8. Cascading constraints

• When a row in the parent table is deleted or updated, it is cascaded to the corresponding row in the child table .
• Helps maintain data consistency between tables.

9. Index constraints

• Restrict the operations that can be performed on indexed columns, such as uniqueness or foreign key constraints.

10. Spatial constraints

• Specify the spatial types and dimensions that the geospatial column can accommodate.

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