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What are Integrity Constraints in SQL?

What are Integrity Constraints in SQL?


Think about you’re the gatekeeper of a society the place each resident and customer should comply with sure guidelines to keep up peace and order. On this planet of databases, these guidelines are often called 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 guarantee knowledge accuracy and consistency like guidelines keep order in a metropolis.
  • Integrity constraints forestall knowledge anomalies, making certain legitimate and constant knowledge references.
  • The 4 primary sorts are entity, area, referential, and examine 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 Essential?

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

Varieties of Integrity Constraints in SQL

There are 4 primary varieties of integrity constraints in SQL, every serving a selected function:

Kind 1:Entity Integrity Constraints

These guarantee every desk row has a singular identifier, sometimes enforced by way of a major key constraint. That is very useful in stopping duplicate entries and ensures a strategy to determine every file uniquely. We will additionally use that attribute to fetch knowledge and arrange 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 singular identifier, stopping duplicate order entries.

Kind 2: Area Constraints

These outline the legitimate values for a specific column. For instance, an age column may need a site constraint proscribing entries to NU. This ensures knowledge conforms to the anticipated format and likewise 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.

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

On this state of affairs, the BookshelfID column within the Books desk turns into a overseas key referencing the BookshelfID major key within the Bookshelves desk. This ensures a e book file solely references a legitimate bookshelf location.

Kind 4: Examine Constraints

These enable for extra complicated validation guidelines on a column or group of columns. You possibly can outline a customized expression that the info should adhere to. This provides better flexibility for implementing 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 all the time optimistic and the StockLevel is rarely destructive.

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

Advantages of Utilizing Integrity Constraints

Listed here are the advantages of utilizing integrity constraints:

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

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

Understanding All Constraints With Examples

Now, we’ll use yet one more instance to know these constraints in higher element – Right here, we now have taken two tables, Departments and Workers, and we now have 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 Workers (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 singular identifier for every file.

    This can fail because of duplicate major key

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

This can fail as a result of non-existent DeptID

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

This can fail because of destructive wage

INSERT INTO Workers (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 Workers (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 Knowledge 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 implementing guidelines that knowledge should adhere to, they forestall errors and inconsistencies that would in any other case result in vital points. Whether or not it’s sustaining distinctive identifiers with major keys, making certain relationships with overseas keys, or implementing particular knowledge ranges with examine 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, and so they:
A. Implement knowledge validation
B. Preserve relationships between tables
C. Stop invalid knowledge entry
D. Embody Major Key, Overseas Key, Distinctive, Examine, and Not Null constraints

Q2. What are the 6 constraints in SQL? 

Ans. A: The six primary constraints in SQL are:
A. Major Key Constraint
B. Overseas Key Constraint
C. Distinctive Constraint
D. Examine Constraint
E. Not Null Constraint
F. Default Constraint

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

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

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

Ans. Knowledge integrity is the general idea of sustaining correct and constant knowledge, whereas integrity constraints are the particular guidelines carried out in SQL to implement knowledge integrity. In different phrases:
A. Knowledge integrity is the aim 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.

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