What are Integrity Constraints in SQL?



Think about you’re the gatekeeper of a society the place each resident and customer should observe sure guidelines to keep up peace and order. On the earth of databases, these guidelines are often known as integrity constraints. Simply as a society thrives when everybody abides by its legal guidelines, a database stays correct and constant when its knowledge adheres to those essential constraints. Intriguing, proper? Additional on this article, we’ll focus on integrity constraints in SQL.

Integrity Constraints in SQL


  • Integrity constraints in SQL guarantee knowledge accuracy and consistency like guidelines keep order in a metropolis.
  • Integrity constraints stop knowledge anomalies, making certain legitimate and constant knowledge references.
  • The 4 fundamental sorts are entity, area, referential, and verify constraints.
  • Sensible examples present how these constraints enhance knowledge accuracy and consistency and cut back errors.
  • Integrity constraints are important for a sturdy and dependable database system, safeguarding knowledge integrity.

Why are Integrity Constraints Vital?

Think about a desk storing details about prospects and their orders. With out constraints, you would possibly find yourself with an order referencing a non-existent buyer! Integrity constraints assist stop such knowledge anomalies by imposing particular guidelines.

Varieties of Integrity Constraints in SQL

There are 4 fundamental kinds of integrity constraints in SQL, every serving a particular goal:

Sort 1:Entity Integrity Constraints

These guarantee every desk row has a novel identifier, sometimes enforced by a main key constraint. That is very useful in stopping duplicate entries and ensures a option to determine every file uniquely. We are able to additionally use that attribute to fetch knowledge and manage knowledge.

Instance of Entity Integrity Constraints

E-commerce Order Desk

  • Desk Identify: Orders
  • Columns:
    • OrderID (integer) Major Key
    • CustomerID (integer)
    • OrderDate (date)
    • TotalAmount (decimal)

On this instance, OrderID is the first key. This ensures every order has a novel identifier, stopping duplicate order entries.

Sort 2: Area Constraints

These outline the legitimate values for a selected column. For instance, an age column may need a website constraint proscribing entries to NU. This ensures knowledge conforms to the anticipated format and in addition undesirable entries within the knowledge which can result in extra issues within the database.

Product Desk

  • Desk Identify: Merchandise
  • Columns:
    • ProductID (integer) Major Key
    • ProductName (textual content)
    • Worth (decimal) NOT NULL
    • StockLevel (integer) NOT NULL

Right here, area constraints are enforced on each Worth and StockLevel columns. The NOT NULL constraints make sure the Worth is just not null.

Sort 3: Referential Integrity Constraints

These keep relationships between tables. A overseas key constraint creates a hyperlink between a column in a single desk (the overseas key) and the first key of one other desk (the referenced desk). This ensures knowledge references in your database are legitimate and constant.

Library Database

  • We are able to prolong the library database to incorporate a Bookshelves desk:
    • Desk Identify: Bookshelves
    • Columns:
      • BookshelfID (integer) Major Key
      • Location (textual content)
      • Capability (integer)
    • We are able to add a overseas key constraint to the Books desk:
      • Desk Identify: Books 
      • Columns:
        • Creator (textual content)
        • Title (textual content)
        • ISBN (textual content) Major Key
        • BookshelfID` (integer) FOREIGN KEY REFERENCES Bookshelves(BookshelfID)

On this situation, the BookshelfID column within the Books desk turns into a overseas key referencing the BookshelfID main key within the Bookshelves desk. This ensures a e-book file solely references a legitimate bookshelf location.

Sort 4: Verify Constraints

These enable for extra complicated validation guidelines on a column or group of columns. You’ll be able to outline a customized expression that the information should adhere to. This presents better flexibility for imposing particular enterprise logic inside your database.

Product Desk

  • Desk Identify: Merchandise
  • Columns:
    • ProductID (integer) Major Key
    • ProductName (textual content)
    • Worth (decimal) CHECK (Worth > 0)
    • StockLevel (integer) CHECK (StockLevel >= 0)

Right here, area constraints are enforced on each Worth and StockLevel columns. The CHECK constraints make sure the Worth is at all times constructive and the StockLevel isn’t damaging.

Additionally Learn: SQL: A Full Fledged Information from Fundamentals to Advance Stage

Advantages of Utilizing Integrity Constraints

Listed here are the advantages of utilizing integrity constraints:

  • Improved Information Accuracy: Stop invalid or faulty knowledge from coming into the database.
  • Enhanced Information Consistency: Guarantee knowledge adheres to outlined guidelines, sustaining consistency throughout tables.
  • Decreased Errors: Implement knowledge validation guidelines, serving to stop errors throughout knowledge manipulation.
  • Stronger Information Relationships: Referential constraints implement relationships between tables, making certain knowledge references are legitimate.
  • Dependable Information Basis: Safeguard the integrity of your knowledge, resulting in extra reliable data.

Additionally learn: Completely different Keys in SQL (Major Key, Candidate Key, International Key)

Understanding All Constraints With Examples

Now, we’ll use yet another instance to know these constraints in higher element – Right here, we’ve got taken two tables, Departments and Staff, and we’ve got used constraints.

-- Create tables

CREATE TABLE Departments (






    FirstName VARCHAR(50) NOT NULL,

    LastName VARCHAR(50) NOT NULL,

    Electronic mail VARCHAR(100) UNIQUE,

    Wage DECIMAL(10, 2) CHECK (Wage > 0),

    DeptID INT,

    FOREIGN KEY (DeptID) REFERENCES Departments(DeptID)


-- Insert pattern knowledge

INSERT INTO Departments (DeptID, DeptName) VALUES

(1, 'HR'),

(2, 'IT'),

(3, 'Finance');

INSERT INTO Staff (EmpID, FirstName, LastName, Electronic mail, Wage, DeptID) VALUES

(101, 'John', 'Doe', '[email protected]', 50000, 1),

(102, 'Jane', 'Smith', '[email protected]', 60000, 2),

(103, 'Mike', 'Johnson', '[email protected]', 55000, 3);
Integrity Constraints in SQL

Examples of Every Constraint

Now, let’s study every constraint:

  1. Major Key Constraint: Ensures a novel identifier for every file.

    This can fail because of duplicate main key

INSERT INTO Departments (DeptID, DeptName) VALUES (1, 'Advertising and marketing');
Primary Key Constraint
  1. International Key Constraint: Maintains referential integrity between tables.

This can fail as a result of non-existent DeptID

INSERT INTO Staff (EmpID, FirstName, LastName, Electronic mail, Wage, DeptID)
VALUES (104, 'Alice', 'Brown', '[email protected]', 52000, 4);
Primary Key Constraint
  1. Distinctive Constraint: Ensures no duplicate values in a column.

    This can fail because of duplicate electronic mail

INSERT INTO Staff (EmpID, FirstName, LastName, Electronic mail, Wage, DeptID)
VALUES (105, 'Bob', 'Wilson', '[email protected]', 54000, 2);
Primary Key Constraint
  1. Verify Constraint: Enforces area integrity by limiting the values in a column.

This can fail because of damaging wage

INSERT INTO Staff (EmpID, FirstName, LastName, Electronic mail, Wage, DeptID)
VALUES (106, 'Carol', 'Davis', '[email protected]', -1000, 3);
Primary Key Constraint
  1. Not Null Constraint: Ensures a column can’t have NULL values.

    This can fail because of NULL FirstName

INSERT INTO Staff (EmpID, FirstName, LastName, Electronic mail, Wage, DeptID)
VALUES (107, NULL, 'Taylor', '[email protected]', 58000, 1);
Primary Key Constraint

These integrity constraints work collectively to keep up knowledge consistency and reliability in your database.

Additionally learn: SQL For Information Science: A Newbie Information!


So, we noticed how integrity constraints assist construct a sturdy and dependable database system. These constraints act as a security web, safeguarding the integrity of your knowledge and making certain its accuracy for future use. By imposing guidelines that knowledge should adhere to, they stop errors and inconsistencies that would in any other case result in important points. Whether or not it’s sustaining distinctive identifiers with main keys, making certain relationships with overseas keys, or imposing particular knowledge ranges with verify constraints, these mechanisms are important for the well being and reliability of your database. As you design and handle your

Incessantly Requested Questions

Q1. What are integrity constraints in SQL? 

Ans. Integrity constraints in SQL are guidelines that guarantee knowledge accuracy and consistency, they usually:
A. Implement knowledge validation
B. Preserve relationships between tables
C. Stop invalid knowledge entry
D. Embrace Major Key, International Key, Distinctive, Verify, and Not Null constraints

Q2. What are the 6 constraints in SQL? 

Ans. A: The six fundamental constraints in SQL are:
A. Major Key Constraint
B. International Key Constraint
C. Distinctive Constraint
D. Verify Constraint
E. Not Null Constraint
F. Default Constraint

Q3. What’s the integrity of information in SQL? 

Ans. Information integrity in SQL means:
A. Information is correct and constant
B. Data stays dependable over time
C. Information is protected against unauthorized modifications
D. Saved knowledge matches its supposed illustration
E. Relationships between knowledge parts are preserved

This fall. What’s knowledge integrity vs integrity constraints? 

Ans. Information integrity is the total idea of sustaining correct and constant knowledge, whereas integrity constraints are the precise guidelines carried out in SQL to implement knowledge integrity. In different phrases:
A. Information integrity is the purpose of making certain knowledge is correct, constant, and dependable.
B. Integrity constraints are the means: particular guidelines and mechanisms in SQL that assist obtain and keep knowledge integrity.
C. Integrity constraints are instruments used to implement and implement knowledge integrity inside a database administration system.