SQL Course Lecture Notes

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• Complete SQL learning session today.
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• Special 20% offer valid until August 21.
• New batch starts on August 31.

SQL Learning Objectives

• Learn SQL from scratch, including commands and practical execution.
• Practice solving questions.

Importance of SQL in Companies

• SQL is widely used in major companies (e.g., Instagram, Uber, Amazon, Netflix) for database access.
• Key skills for software engineering, data-related jobs, and development roles.

Database Basics

What is a Database?

• Collection of data in a structured format.
• Easily accessible for searching, adding, and deleting data.

Database Management System (DBMS)

• Software application for managing databases.
• Interacts with databases to perform CRUD operations (Create, Read, Update, Delete).

Types of Databases

• Relational Databases: Data stored in tables (e.g., MySQL, SQL Server).
• Non-Relational Databases: Data stored in a non-tabular format (e.g., MongoDB).

SQL Basics

SQL Definition

• SQL: Structured Query Language.
• Used to communicate with databases.

CRUD Operations in SQL

1. Create: Create a new database or table.
   • Example: CREATE DATABASE db_name;
2. Read: Retrieve data from a database.
   • Example: SELECT * FROM table_name;
3. Update: Modify existing data.
   • Example: UPDATE table_name SET column_name = value WHERE condition;
4. Delete: Remove data from a database.
   • Example: DELETE FROM table_name WHERE condition;

Basic SQL Commands

• Data types (e.g., INT, VARCHAR, DATE).
• Constraints (e.g., PRIMARY KEY, FOREIGN KEY, NOT NULL).

Advanced SQL Concepts

Joins in SQL

• Inner Join: Returns records that have matching values in both tables.
  • Example: SELECT * FROM table1 INNER JOIN table2 ON table1.column = table2.column;
• Left Join: Returns all records from the left table and matched records from the right table.
  • Example: SELECT * FROM table1 LEFT JOIN table2 ON table1.column = table2.column;
• Right Join: Returns all records from the right table and matched records from the left table.
  • Example: SELECT * FROM table1 RIGHT JOIN table2 ON table1.column = table2.column;
• Full Join: Combines the results of both left and right joins.
  • Example: SELECT * FROM table1 FULL JOIN table2 ON table1.column = table2.column;

Subqueries

• Subqueries (inner queries) are queries nested inside another query.
  • Example: SELECT * FROM table1 WHERE column IN (SELECT column FROM table2);

Views in SQL

• Views are virtual tables created from SQL queries.
  • Example: CREATE VIEW view_name AS SELECT column1, column2 FROM table_name;

Practical Examples

1. Use SQL to calculate average marks or find specific records based on conditions.
2. Apply joins to combine data from multiple tables.
3. Implement subqueries for complex queries in SQL.

SQL Practice

• Students should practice SQL commands and concepts regularly to strengthen understanding and skills.