Module 3: Integrity Constraints in MySQL Databases

A Comprehensive Guide to Using and Enforcing Integrity Constraints.

Importance of Integrity Constraints

• Ensuring Data Accuracy

• Maintaining Data Consistency

• Ensuring Data Reliability

• Avoiding Logical Errors

• Reducing Redundancy

Ensuring Data Accuracy

Integrity constraints ensure the data is accurate by preventing invalid entries.

Maintaining Data Consistency

Constraints enforce rules across tables, especially in relational databases.

Ensuring Data Reliability

Prevents data corruption by enforcing business rules at the database level.

Avoiding Logical Errors

Prevents actions that could break relationships between data (e.g., orphaned records).

Reducing Redundancy

Prevents duplicate or irrelevant data entries.

Types of Integrity Constraints in MySQL

• Primary Key (PK)

• Foreign Key (FK)

• Unique Constraint

• NOT NULL

• Check Constraint

• Default Constraint

Primary Key (PK)

Guarantees unique identification of each record.

Foreign Key (FK)

Links tables and enforces relationships.

Unique Constraint

Prevents duplicate values in specific columns.

NOT NULL

Ensures that a field cannot be left empty.

Check Constraint

Validates that data in a column meets specific criteria (MySQL 8.0+).

Default Constraint

Assigns a default value if no value is provided.

Optimizing Table Design in MySQL

• Choose the Right Data Types

• Appropriate Field Sizes

• Normalization

• Indexes

ON DELETE CASCADE

Automatically deletes child records when the parent record is deleted.

ON UPDATE CASCADE

Automatically updates child records when the parent key changes

Why Use Cascades?

• Simplifies data management when relationships exist.

• Prevents orphaned records (records in child tables with no matching parent).

Additional MySQL Constraints & Best Practices

• Default Constraints: Assign default

  values to fields when no data is provided.

• Indexing for Faster Queries: Add indexes to

  columns frequently used in WHERE clauses for faster query performance.

• Preventing Data Anomalies: Use CHECK

  constraints, foreign keys, and validation logic to prevent data anomalies (e.g., entering a future date of birth).

• Foreign Key Options: Use SET NULL to set

  foreign key fields to NULL when the parent

  record is deleted. (ON DELETE SET NULL)

Integrity Constraints Ensure Data Reliability

Use constraints to maintain the accuracy and consistency of your data.

Cascade Actions Are Powerful

Use them carefully to avoid unwanted data deletion or updates.

Enforce Integrity in Both Databases and Code:

MySQL constraints are the first line of defense, but application-level validation is also important.

Optimal Table Design Matters

Correct data types, field sizes, and constraints lead to efficient and reliable databases.