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.
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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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