Integrity Constraints in DBMS Explained

Introduction to Integrity Constraints in DBMS

Integrity constraints in DBMS can be defined as a collection of rules used to ensure the quality of information. This assures that data insertion, modification, and other operations do not affect data integration. There are mainly four types of integrity constraints, namely, domain constraint, referential integrity constraint, entity integrity constraint, and key constraint. If you want to learn more about integrity constraints in DBMS, enrol in a Full-Stack Software Development Bootcamp today!

Importance of Integrity Constraints in DBMS

Integrity constraints play a crucial role in a DBMS for ensuring the accuracy, consistency, and reliability of the data stored in a database. Here are some key reasons highlighting the importance of integrity constraints:

  • Data Accuracy: Integrity constraints enforce rules that ensure the correctness and accuracy of the data. Constraints prevent the insertion of invalid or inappropriate values into tables, maintaining the integrity of the data. Data entry errors and inconsistencies can be minimised or eliminated by defining constraints such as NOT NULL, UNIQUE, and CHECK.
  • Data consistency: Integrity constraints establish relationships between tables, ensuring consistency across related data. For example, foreign key constraints maintain referential integrity, preventing the creation of orphaned records and ensuring that foreign vital values correspond to valid primary key values. This promotes consistency and coherence in the database.
  • Data reliability: Integrity constraints help guarantee the reliability and trustworthiness of the data. Constraints prevent the occurrence of logical inconsistencies, contradictory data, or conflicts that may arise due to erroneous or unauthorised data modifications. By enforcing constraints, the DBMS ensures that only valid and reliable data is stored, enhancing the overall quality of the database.
  • Data validation: Integrity constraints act as a means of data validation by imposing specific rules or conditions on the data. Constraints such as CHECK constraints allow the definition of data validation rules based on specific criteria, such as data type, range, format, or logical conditions. This helps to ensure that the data entered into the database meets the predefined criteria and business rules.
  • Data security: Integrity constraints contribute to data security by preventing unauthorised or inappropriate modifications to the database. Constraints help enforce access control and data governance policies. This limits data modifications to authorised users. Also, it ensures that only valid changes are made. This helps to protect the integrity and confidentiality of the data.
  • Database performance: Properly defined and enforced integrity constraints can improve database performance. By ensuring the consistency and validity of the data, constraints enable the DBMS to optimise query execution plans. They also perform efficient data retrieval and manipulation operations. Constraints can also enable the use of indexing and other performance-enhancing techniques.

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Types of Integrity Constraints in DBMS

In DBMS, four types of integrity constraints play a crucial role in maintaining data integrity and enforcing business rules. 

  • Domain Constraint

A domain constraint defines the valid range of values that a column can hold. It specifies a column’s data type, format, and allowable values. By enforcing domain constraints, data consistency and validity can be ensured, preventing inappropriate or inconsistent data insertion into a column.

  • Referential Integrity Constraint

The referential integrity constraint establishes relationships between tables by enforcing consistency in related data. It ensures that one table’s values in a foreign key column(s) correspond to the primary key values in another table. This constraint prevents the creation of orphaned records and maintains the integrity of data associations between tables.

  • Entity Integrity Constraint

The entity integrity constraint focuses on the uniqueness of primary key values within a table. It ensures that a table’s primary key column(s) contains unique and non-null values. This constraint guarantees the identification and differentiation of individual records within a table.

  • Key Constraint

The key constraint determines the uniqueness of values within a column or a combination of columns. It can be applied to designate a candidate key or a primary key. The key constraint prevents duplicate values in the specified column(s) and ensures that each record can be uniquely identified. Here are the types of key constraints:

  • NOT NULL Constraint

The NOT NULL constraint specifies that a column in a table must not contain any null values. It ensures that a particular attribute or field cannot be left empty or undefined for any record in the table. 

  • UNIQUE Constraint

The UNIQUE constraint ensures that the values in a specific column(s) are unique across all the records in a table. It allows for the insertion of null values. However, it allows only one instance of a non-null value. 

  • PRIMARY KEY Constraint

The PRIMARY KEY constraint identifies each record in a table uniquely. It enforces the uniqueness and non-null property of one or more columns in a table. A primary key can consist of a single column or a combination of multiple columns.

  • FOREIGN KEY Constraint

The FOREIGN KEY constraint creates a relationship between two tables based on the values of a column or columns. It helps maintain referential integrity by enforcing that the values in a specific column(s) of one table correspond to those of a primary key in another table. 

  • CHECK Constraint

The CHECK constraint explains a condition that must be satisfied for the values in a column(s). It allows you to limit the range of acceptable values based on a specific condition or expression.

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Difference Between Constraints and Triggers in DBMS

Constraints in DBMS Triggers in DBMS
Constraints are predefined rules that govern the data integrity and behaviour of the database. Triggers are database objects automatically executed in response to specific events or actions.
Constraints are applied to tables and columns. Triggers are associated with tables or views.
Constraints are evaluated and enforced automatically during data modification operations. Triggers are fired based on defined events or actions, such as INSERT, UPDATE, DELETE, or other user-defined events.
Examples of constraints include NOT NULL, UNIQUE, PRIMARY KEY, FOREIGN KEY, and CHECK constraints. Examples of triggers include BEFORE INSERT, AFTER UPDATE, and INSTEAD OF DELETE triggers.
Constraints are declarative and specified when the table is created or altered. Triggers are procedural and defined separately from the table structure.
Constraints help maintain data integrity and enforce predefined rules for data manipulation. Triggers are often used to implement complex business rules, audit, log, or maintain derived data.
Constraints are checked immediately during data modification, ensuring immediate enforcement. Triggers are executed after the triggering event occurs and can perform actions before or after the event.
The database management system manages constraints. Triggers are typically created and managed by developers or database administrators. 


Examples of Using Integrity Constraints in DBMS

Here are some examples of using integrity constraints in a DBMS:

NOT NULL Constraint: Ensuring the “email” column in a “users” table cannot be empty. This requires all users to provide an email address.

UNIQUE Constraint: Ensuring the “username” column in a “users” table contains unique values. This prevents multiple users from having the same username.

PRIMARY KEY Constraint: Setting the “customer_id” column in a “customers” table as the primary key. This is to identify each customer uniquely.

FOREIGN KEY Constraint: Establishing a relationship between a “customer_id” column in an “orders” table and the corresponding “customer_id” column in a “customers” table. This ensures that all orders are associated with valid customers.

CHECK Constraint: Specifying a CHECK constraint ensures that a “salary” column in an “employees” table only contains positive values, preventing negative salaries from entering.

These examples demonstrate how integrity constraints can be applied in different scenarios to enforce data integrity in DBMS, maintain relationships between tables, and impose specific conditions or rules on data stored in a DBMS.

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As illustrated in this blog, integrity constraints are essential in ensuring the accuracy of the database. This is an area of software development and database management. You could enrol in the Executive Post Graduate Software Development Programme in Full-Stack Development by upGrad. It is a 13-month-long programme with world-class faculty and industry experts. The curriculum is extensive and covers software development and database management elements from scratch. Enquire today to know more! 

Why is it better to use an integrity constraint?

Integrity constraints act as safeguards against accidental damage to the database. This is done by ensuring that data insertion, updating, and other processes adhere to rules that maintain data integrity. They enforce restrictions and validations. This prevents the introduction of inconsistent or invalid data that could compromise the accuracy and reliability of the database.

Is integrity a primary key constraint?

No, integrity is not a primary key constraint. Integrity refers to the overall quality and reliability of the data in a database. In contrast, the primary key constraint is a specific type of integrity constraint. This ensures uniqueness and non-null values in one or more columns of a table.

Which constraint creates referential integrity in DBMS?

A FOREIGN KEY constraint is a referential integrity constraint in DBMS. A logical rule establishes referential integrity between tables by specifying that values in one or more columns in one table must match the primary key values in another table.

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