1. Joins (SQL Joins)

At Appin Technology, students learn how to combine data from multiple tables using Joins.

A Join is used to retrieve related data from two or more tables based on a common column.

Types of Joins: INNER JOIN

Returns only the rows where data exists in both tables.

Use case: Fetching students who are enrolled in a course.

LEFT JOIN

Returns all records from the left table and matching records from the right table. If no match exists, NULL is returned.

RIGHT JOIN

Returns all records from the right table and matching records from the left table.

FULL JOIN

Returns all records from both tables, whether they match or not.

Why Appin Technology teaches Joins?

Efficient data retrieval

Real-world database design

Faster application performance

1. Subqueries

A Subquery is a query written inside another SQL query.

At Appin Technology, students use subqueries to handle complex data conditions.

Example:

Finding employees whose salary is greater than the average salary.

Subqueries can be used in:

SELECT

WHERE

FROM clauses

Types:

Single-row subqueries

Multi-row subqueries

Correlated subqueries

Benefits:

Improves query flexibility

Handles complex logic

Reduces multiple queries

1. CRUD Operations

CRUD operations form the foundation of database-driven applications, and Appin Technology ensures strong hands-on practice.

CRUD Meaning: Operation Description Create Insert new records Read Retrieve existing records Update Modify data Delete Remove data CRUD in SQL:

INSERT

SELECT

UPDATE

DELETE

CRUD in Django ORM:

create()

get()

filter()

update()

delete()

Every real-time application uses CRUD operations, which is why Appin Technology emphasizes practical training.

1. ORM in Django

ORM (Object Relational Mapping) allows developers to interact with databases using Python objects instead of SQL queries.

At Appin Technology, Django ORM is taught with real-time projects.

Advantages of Django ORM:

No need to write raw SQL

Secure against SQL injection

Faster development

Database independent

Common ORM Methods:

objects.all()

objects.get()

objects.filter()

objects.create()

objects.update()

objects.delete()

ORM simplifies backend development and increases productivity.

1. Model Relationships (Django)

Model relationships define how database tables are connected.

Relationship Types taught at Appin Technology: One-to-One Relationship

One record in a table relates to one record in another table. Example: User ↔ Profile

One-to-Many Relationship

One record relates to many records. Example: Instructor ↔ Students

Many-to-Many Relationship

Many records relate to many records. Example: Students ↔ Courses

Why relationships matter:

Proper data organization

Reduced redundancy

Easy data access

1. Migrations in Django

Migrations are used to keep the database schema synchronized with Django models.

At Appin Technology, students learn safe and version-controlled database updates.

Common Migration Commands: python manage.py makemigrations python manage.py migrate

Benefits:

Track database changes

Apply updates safely

Maintain data consistency

1. MongoDB Basics

MongoDB is a NoSQL database used for modern scalable applications.

Key MongoDB Concepts: Relational DB MongoDB Table Collection Row Document Column Field Example Document: { "name": "Kumar", "course": "Full Stack Development", "skills": ["Python", "Django", "MongoDB"] }

MongoDB Features:

Schema-less design

High scalability

Flexible data structure

High performance

MongoDB CRUD Operations:

insertOne()

find()

updateOne()

deleteOne()