RDBMS Constraints

Introduction

• Database Constraints are typically enforced by the database management system (DBMS) and play a crucial role in ensuring data consistency and accuracy.

Definition

• Database constraints are rules and restrictions applied to data in a database to ensure data integrity, accuracy, and consistency. 

Characteristics

• Database constraints define certain conditions that data must meet, preventing the insertion, modification, or deletion of data that would violate these rules.
• Database constraints are an integral part of the database for maintaining data quality, preventing inconsistencies, and enforcing business rules within the database.
• Database constraints help to ensure that the data adheres to predefined conditions, thus enhancing data reliability and integrity.

Types of RDBMS Constraints

• Relational Database Management Systems (RDBMS) use different types of constraints to enforce rules and maintain data integrity.
• By following constraints rules which help in maintaining data accuracy, consistency, and relationships within the database, ensuring that the data is stored in the tables.
• There are several types of constraints commonly used in RDBMS:

• • Primary Key Constraint:
    • This constraint uniquely identifies each record in a table.
    • It ensures that the column or combination of columns marked as the primary key has unique values and cannot contain NULL (empty) values.
  • Foreign Key Constraint:
    • A foreign key establishes a relationship between two tables. It ensures referential integrity by enforcing that values in a column (or combination of columns) in one table match values in another table’s primary key.
    • This constraint maintains consistency between related tables.
  • Unique Constraint:
    • This constraint is similar to a primary key, a unique constraint ensures that the values in a column (or combination of columns) are unique, but it can allow NULL values, unlike a primary key.
  • Check Constraint:
    • Check constraints allow us to define specific rules or conditions that data in a column must meet.
    • For example, we can define a check constraint to ensure that values entered in a column fall within a specific range or satisfy certain conditions.
  • Not Null Constraint:
    • This constraint ensures that a column cannot contain NULL values.
    • It mandates that every entry in the specified column must have a value.