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    •  Integrity Constraints in DBMS 

     Integrity Constraints kya hote hain?

    Integrity Constraints kuch rules hote hain jo hum database par lagate hain taaki data:

    • -> Sahi ho (Valid)

    • -> Consistent ho (Maitlab, logically theek ho)

    • -> Reliable ho (Galat ya missing na ho)

    Ye constraints ensure karte hain ki koi bhi invalid ya galat data database me na jaaye.

     Example Samjho:

    Maan lo ek Student table hai. Aap chahte ho ki:

    • Har student ka ID unique ho

    • Naam khaali (empty) na ho

    • Age 0 se zyada ho

     In sab rules ko Integrity Constraints kehte hain.

     Types of Integrity Constraints

    Type Kya kaam karta hai?
    1. Domain Constraint Data ka type check karta hai
    2. Entity Integrity Primary key ko unique aur non-null banata hai
    3. Referential Integrity Tables ke beech relation maintain karta hai
    4. Unique Constraint Unique values enforce karta hai
    5. Not Null Constraint NULL (empty) values ko allow nahi karta
    6. Check Constraint Custom condition lagata hai value par

     1. Domain Constraint

    Ye ensure karta hai ki column me correct data type ka hi value aaye.

     Example:

    CREATE TABLE Student (
    ID INT,
    Name VARCHAR(50),
    Age INT
    );

    • ID sirf integer le sakta hai

    • Name max 50 characters ka text

    • Age me text nahi aana chahiye

     Iska kaam: Galat data type ko rokna

     2. Entity Integrity Constraint

    Ye ensure karta hai ki har row ka ek unique aur non-null primary key ho.

     Example:

    CREATE TABLE Student (
    ID INT PRIMARY KEY,
    Name VARCHAR(50)
    );
     

     Rules:

    • Har ID unique ho

    • ID null nahi ho sakta

     Diagram:

    +----+------+
    | ID | Name |
    +----+------+
    | 1 | Riya  |
    | 2 | Aman  |
    |   | X (NULL not allowed) |
    | 1 | X (Duplicate not allowed) |
     

     3. Referential Integrity Constraint

    Ye foreign key ka use karke tables ke beech relation banata hai.

     Example:

    Student Table:

    CREATE TABLE Student (
    ID INT PRIMARY KEY,
    Name VARCHAR(50)
    );
     

    Course Table:

    CREATE TABLE Course (
    CourseID INT PRIMARY KEY,
    StudentID INT,
    FOREIGN KEY (StudentID) REFERENCES Student(ID)
    );
     

     Rule:

    • Course table me aisa StudentID nahi ho sakta jo Student table me exist nahi karta.

     Diagram:

    Student Table  
    +----+------+ 
    | ID | Name | 
    +----+------+ 
    | 1  | Riya | 
    | 2  | Aman | 
    +----+------+
     
    Course Table
    +------+-----------+
    | C_ID | StudentID |
    +------+-----------+
    | 101  | 1         |
    | 102  | 3 X (3 exist nahi karta)

     4. Unique Constraint

    Ye ensure karta hai ki column ke saare values unique ho, lekin null value allowed hai.

     Example:

    CREATE TABLE Employee (
    EmpID INT,
    Email VARCHAR(100) UNIQUE
    );
     

     Rule:

    • Do employees ka email same nahi ho sakta.

     5. NOT NULL Constraint

    Ye ensure karta hai ki column me NULL (khaali) value nahi aaye.

     Example:

    CREATE TABLE Student (
    ID INT,
    Name VARCHAR(50) NOT NULL
    );
     

     Rule:

    • Name column me value dena zaroori hai.

     6. Check Constraint

    Ye ek custom condition lagata hai values ke liye.

     Example:

    CREATE TABLE Student (
    ID INT,
    Age INT CHECK (Age >= 18)
    );
     

     Rule:

    • Age 18 ya usse zyada honi chahiye.

     Wrong Query:

    INSERT INTO Student (ID, Age) VALUES (1, 16); -- Not allowed
     

     Summary Table

    Constraint Type Kya ensure karta hai?
    Domain Constraint Correct data type aana
    Entity Integrity Primary key unique & non-null ho
    Referential Integrity Tables ke relations valid ho
    Unique Constraint Unique values ho column me
    Not Null Constraint Null value na aaye
    Check Constraint Condition satisfy ho
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