SQL Notes – Queries, Joins & Optimization
1. Introduction to SQL
SQL (Structured Query Language) is the standard language used to interact with
relational databases. It is declarative in nature — you describe the result you want,
and the database engine determines the best way to produce it.
Primary Purpose: Managing, retrieving, and modifying data stored in relational
database systems.
Industry Importance: SQL remains universally relevant in software development,
analytics, business intelligence, and backend systems because of its reliability and
efficiency.
2. SQL Basics & Core Components
2.1 Common Data Types
• INT – Whole numbers (age, employee_id)
• VARCHAR – Variable-length strings (name, email)
• DATE – Date values (birth_date, join_date)
• FLOAT – Decimal values (price, rating)
• BOOLEAN – True/False values (is_active)
2.2 Essential SQL Commands (CRUD Operations)
• CREATE – Creates database objects
• INSERT – Adds new records
• UPDATE – Modifies data
• DELETE – Removes records
• SELECT – Retrieves data
3. SELECT Queries
3.1 Basic Syntax
1. Introduction to SQL
SQL (Structured Query Language) is the standard language used to interact with
relational databases. It is declarative in nature — you describe the result you want,
and the database engine determines the best way to produce it.
Primary Purpose: Managing, retrieving, and modifying data stored in relational
database systems.
Industry Importance: SQL remains universally relevant in software development,
analytics, business intelligence, and backend systems because of its reliability and
efficiency.
2. SQL Basics & Core Components
2.1 Common Data Types
• INT – Whole numbers (age, employee_id)
• VARCHAR – Variable-length strings (name, email)
• DATE – Date values (birth_date, join_date)
• FLOAT – Decimal values (price, rating)
• BOOLEAN – True/False values (is_active)
2.2 Essential SQL Commands (CRUD Operations)
• CREATE – Creates database objects
• INSERT – Adds new records
• UPDATE – Modifies data
• DELETE – Removes records
• SELECT – Retrieves data
3. SELECT Queries
3.1 Basic Syntax
