What types of constraints are commonly used in mysql?

Commonly used constraint types in MySQL: Primary key constraints: uniquely identify each row. Foreign key constraints: Ensure data referential integrity. Unique constraint: Ensure that the values ​​in the column are unique. Non-null constraint: ensures that the column does not contain null values. Default constraint: Specifies the default value of the column. Check constraints: Custom validation of values ​​in columns. Index constraints: Create indexes to optimize data retrieval speed. External key constraints: Reference data from an external data source. Row-level security constraints: restrict access to specific rows of data. Trigger constraints: perform custom operations during data manipulation.

Commonly used constraint types in MySQL

Constraints in MySQL are used to ensure data integrity and can ensure data consistency, accuracy and reliability. The following are commonly used constraint types in MySQL:

1. Primary key constraints

• define the columns that uniquely identify each row in the table.
• cannot be empty and duplicate values ​​are not allowed.
• Usually used for foreign key associations and indexing.

2. Foreign key constraints

• reference the primary key of another table.
• Ensure referential integrity between data.
• When data in the main table is deleted or updated, it can be cascaded to delete or update related data from the table.

3. Unique constraints

• Ensure that the values ​​in the column are unique.
• Null values ​​are allowed, but duplicates are not allowed.
• For columns that often need to be searched, unique indexes can be established to improve query performance.

4. Non-null constraint

• Ensure that the column cannot contain null values.
• Mandatory data integrity to avoid errors caused by data loss.

5. Default constraints

• Specify a default value for the column.
• When inserting a new row, if a column value is not specified, the default value is used.

6. Check constraints

• Perform custom validation on the values ​​in the column.
• You can use operators (such as >,

7. Index constraints

• Create indexes to optimize data retrieval speed.
• You can create indexes on primary key, foreign key and unique constraint columns, or use custom indexes.

8. External key constraints

• Reference data in an external database or file.
• Ensure consistency between data and other systems.

9. Row-level security constraints

• Restrict access to specific rows of data.
• Data can only be accessed or modified by users with appropriate permissions.

10. Trigger constraints

• Perform custom operations when inserting, updating, or deleting data.
• Can be used to implement complex business rules or maintain data integrity.

The above is the detailed content of What types of constraints are commonly used in mysql?. For more information, please follow other related articles on the PHP Chinese website!