Fundamentals of SQL and Its Evolution

Aug 8, 2024

Introduction to SQL

Overview

  • Discussing SQL and its importance in databases.
  • Importance of historical context and syllabus for students.

What is SQL?

  • SQL: Structured Query Language.
  • Used for communication between users and databases.
  • Enables interaction with structured data through tables (relational databases).

History of SQL

  • 1970: EF Codd introduced the relational model of databases.
    • Published a paper on the concept of storing data in tables.
    • Utilized relational algebra and tuple relational calculus.
  • IBM's Role:
    • Converted Codd's theoretical model into a practical language, initially named SEQUEL (Simple English Query Language).
    • Later renamed to SQL (Structured Query Language).
  • Evolution of SQL and emergence of competitors like Oracle, Microsoft SQL Server, and IBM DB2.

Current Trends

  • Contemporary data is predominantly unstructured (90%).
  • Introduction of NoSQL technologies for handling unstructured data (e.g., MongoDB, Spark).

Characteristics of SQL

  • Domain Specific Language:
    • Used specifically for relational databases.
  • Declarative Language:
    • Focuses on what to do, not how to do it (contrasts with procedural languages).

SQL Commands

  • Types of SQL commands include:
    • DDL (Data Definition Language)
    • DML (Data Manipulation Language)
    • DCL (Data Control Language)
    • TCL (Transaction Control Language)
  • Key concepts:
    • Keys: Primary key, Foreign key, Candidate key.
    • Constraints: Not null, Default, Unique.

Operators in SQL

  • Common operators include:
    • IN, BETWEEN, NOT IN, EXISTS, NOT EXISTS.

Practical Application of SQL

  • Example: IRCTC database for train bookings, which uses SQL to manage structured data in tables.

Advanced SQL Concepts

  • Clauses: ORDER BY, GROUP BY, HAVING.
  • Aggregate Functions: COUNT, SUM, AVG, MAX, MIN.
  • Joins and Nested Queries:
    • Essential for combining data from multiple tables.
    • Important for placements and competitive exams.

PL/SQL

  • Procedural Language extension for SQL.
  • Combines declarative and procedural components.
    • Allows creation of triggers, functions, cursors, and procedures.

Conclusion

  • Understanding SQL basics is crucial for database management, higher competitive exams, and placements.
  • Importance of mastering joins and nested queries for practical applications.