SQL Tutorial - Full Database Course for Beginners

Overview of SQL and Databases

• SQL (Structured Query Language): Language used to interact with relational database management systems (RDBMS).
• RDBMS: Software application to create and manage databases.
• Course Structure:
  • Basics of databases and SQL.
  • Installation of MySQL (popular for beginners).
  • Writing basic SQL queries (CRUD operations).
  • Advanced techniques and database schema design.

What is a Database?

• Database (DB): Collection of related information.
  • Examples: Phonebook, shopping lists, social media user data.
• Storage Methods:
  • On paper (manual lists).
  • Digitally on computers.
  • Mentally (in memory).

Types of Databases

1. Relational Databases: Organizes data in tables (rows and columns).
   • Example: MySQL, Oracle, PostgreSQL.
2. Non-Relational Databases: Any database not structured in tables.
   • Examples: Document databases, key-value stores.

Core Concepts of Relational Databases

• Tables: Structure to store data (e.g., Student table).
• Keys:
  • Primary Key: Uniquely identifies a row (e.g., Student ID).
  • Foreign Key: Links to another table (e.g., branch ID).
• CRUD Operations:
  • Create, Read, Update, Delete data.

SQL Basics

• SQL Commands:
  • SELECT: Retrieve data.
  • INSERT: Add data.
  • UPDATE: Modify existing data.
  • DELETE: Remove data.

Installing MySQL

• Install MySQL through the official website and set up a local server.
• Optional: Use a SQL editor like PopSQL for writing queries.

Creating Tables and Inserting Data

• Data Types:
  • INT, VARCHAR, DATE, DECIMAL, etc.
• Creating Tables:
  • Use CREATE TABLE syntax with defined data types.
• Inserting Data:
  • Use INSERT INTO syntax to add entries to tables.

Updating and Deleting Data

• Updating: Use UPDATE command with WHERE to specify conditions.
• Deleting: Use DELETE FROM with WHERE to remove entries.

Basic Queries

• Utilize SELECT, WHERE, ORDER BY, and LIMIT to retrieve specific data.
• Use DISTINCT to filter unique results.

JOINs

• JOIN: Combine rows from two or more tables based on related columns.
  • Types of JOINs:
    1. INNER JOIN: Only matching rows.
    2. LEFT JOIN: All rows from left table, matching rows from right.
    3. RIGHT JOIN: All rows from right table, matching rows from left.
    4. FULL OUTER JOIN: All rows from both tables (not supported in MySQL).

Nested Queries

• Nested Queries: A query within another query, often using results from one to filter another.
• Example: Get employees who sold more than $30,000.

Triggers

• Trigger: A block of SQL code executed automatically upon certain events (e.g., INSERT, UPDATE).
• Useful for automating tasks and maintaining data integrity.

ER Diagrams

• ER Diagram: Visual representation of the database schema, illustrating entities and relationships.
• Composed of entities (tables), attributes (columns), and relationships (connections).

Converting ER Diagrams to Schemas

• Steps to convert ER diagrams into database tables:
  1. Map regular entity types to tables.
  2. Map weak entity types (with composite keys).
  3. Define binary relationships using foreign keys.
  4. Handle one-to-many and many-to-many relationships.
  5. Define attributes and constraints in tables.

Conclusion

• Practice designing ER diagrams and converting them into schemas to solidify understanding of SQL and databases.