Integrity Constraints

The constraints you listed are Integrity Constraints in DBMS/RDBMS. They help maintain the accuracy and consistency of data.

1. NOT NULL Constraint

Ensures that a column cannot have a NULL (empty) value.

Example:

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

Here, the Name column must contain a value.

2. UNIQUE Constraint

Ensures that all values in a column are unique.

Example:

CREATE TABLE Student (
    StudentID INT,
    Email VARCHAR(100) UNIQUE
);

No two students can have the same email address.

3. PRIMARY KEY Constraint

Uniquely identifies each record in a table.

Properties:

• Must be unique
• Cannot be NULL
• Only one primary key per table

Example:

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

StudentID uniquely identifies each student.

4. FOREIGN KEY Constraint

Establishes a relationship between two tables.

Example:

Student Table

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

Course Table

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

Here, StudentID in the Course table refers to StudentID in the Student table.

Summary Table

Example Combined

CREATE TABLE Student (
    StudentID INT PRIMARY KEY,
    Name VARCHAR(50) NOT NULL,
    Email VARCHAR(100) UNIQUE
);

CREATE TABLE Result (
    ResultID INT PRIMARY KEY,
    StudentID INT,
    Marks INT,
    FOREIGN KEY (StudentID)
    REFERENCES Student(StudentID)
);

In this example:

• StudentID → PRIMARY KEY
• Name → NOT NULL
• Email → UNIQUE
• StudentID in Result → FOREIGN KEY