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How many types of constraints are there in mysql?

2024-04-27 09:30:39862browse

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.

How many types of constraints are there in mysql?

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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