Difference between Entity constraints, Referential constraints and Semantic constraints

Last Updated : 15 Jul, 2025

Constraints are used in relational databases to follow the standards of the database and guarantee that the data is valid. Users are usually confused about various kinds of constraints most of which include entity constraints, referential constraints and semantic constraints.

In this article, We will learn about the Difference between Entity constraints, Referential constraints and Semantic constraints and so on.

What is Entity constraints?

These constraints are given within one table. The entity constraints are primary key, foreign key, unique. Entity constraints are those constraints that limit the data entered in any one cell or entity of the table at a time.

These constraints mostly revolve around the issue of variance, which is a measure of the distinctive authenticity of the data.

Example:

create table student (rollnumber int primary key, name varchar2(30), course varchar2(10));
Insert into student values(111, 'ABC', 'Chemical');
Insert into student values(112, 'JJP', 'Mech');

Output:

Rollnumber	Name	Course
111	ABC	Chemical
112	JJP	Mech

These values are inserted in the table. Suppose a value given below is inserted :

Insert into student values(111, 'MAB', 'EEE');

It gives an error as the roll-number is enforced a primary key constraint that refrains from duplication. These constraints ensures to maintain uniqueness in the tables to avoid duplication's.

Types of Entity Constraints

Primary Key Constraint: It Provides a means of identifying uniqueness for each row in a table.
Unique Constraint: Similar to a primary key but a column can contain one NULL value.
NOT NULL Constraint: It Blocks the possibility of entering NULL values into a column.

Advantages of Entity Constraints

Data Integrity: There is no repetition or entry of invalid data into the record book.
Improved Searchability: It Retrieves data faster since data must have unique keys to be put into the database.
Consistency: Provids for rational and coherent data input and storage.

Disadvantages of Entity Constraints

Overhead: It May result in delays when working on insert and update processes.
Rigidity: Makes it a little difficult when it comes to data insertion.

What is Referential constraints?

These constraints are used for referring other tables to enforce conditions on the data. The widely used referential constraint is foreign key. Referential integrity guarantees referential integrity, that is, the referential link between tables is consistent.

They keep the relationship between tables intact as keys in one table refer to keys in other tables at the same time.

Example:

create table marks (rollnumber int, name varchar2(30), course varchar2(30)
references student, marks int);

A table is created with a constraint that the marks should be rewarded to those students that are pursuing courses stated in the student table only. If a user tries to enter a value that doesn't exist, it returns an error.

Types of Referential Constraints

Foreign Key Constraint: It Checks that a column (or set of columns) points to a row in another table (often used in HDFS).

Advantages of Referential Constraints

Maintains Data Relationships: It helps in maintaining integrity of reference between tables always.
Cascading Updates/Deletes: It Corrects related rows or deleted to ensure the data recorded in the table is synchronized with other applications.

Disadvantages of Referential Constraints

Complexity: It Introduces difficulties in managing a database.
Performance Overhead: May cause a deceleration of operations that involve related tables.

What is Semantic constraints?

Datatypes are the semantic constraints enforced in a table. Datatypes help the data segregate according to its type. Semantic constraints are rules that capture the meaning or the context of the data. Another type of business rules they implement are not structure related rather they are logical correctness of data.

Example :

A name is a combination of different letters. We can place the name column in the char datatype yet char doesn't satisfy the condition thereby varchar is preferably used for name.

name varchar2(30);

Examples of Semantic Constraints

Age Validation: It Verifying a person’s age to be greater than a certain value.
Salary Constraints: A provision that no salary can be more than a set amount for some positions.

Advantages of Semantic Constraints

Business Logic Enforcement: Confirms that all data agreed to the business rules set.
Higher Data Quality: Enhances the work’s quality since the data is made relevant and more correct.

Disadvantages of Semantic Constraints

Complex Rule Definition: They can easily be evaded and thus become hard when setting rules on them.
Application-Specific: It May need to be updated from time to time whenever there is a change in business requirements.