Introduction to SQL

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SELECT <column_name>
FROM <table_name>
WHERE <condition>;

SELECT <column_name>

FROM <table_name>

WHERE <condition>;

Language	Full Form	Purpose	Commands
DDL	Data Definition Language	Defines database structure	CREATE, ALTER, DROP, TRUNCATE, RENAME
DML	Data Manipulation Language	Modifies data	INSERT, UPDATE, DELETE
DQL	Data Query Language	Retrieves data	SELECT
DCL	Data Control Language	Controls access	GRANT, REVOKE
TCL	Transaction Control Language	Manages transactions	COMMIT, ROLLBACK, SAVEPOINT

Bharath Kumar

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Introduction to SQL

What is SQL?

SQL is also referred to as:

● Structured Query Language

● Syntax Query Language

● Sequential Query Language

It is mainly used to interact with structured databases where data is stored in tables consisting of rows and columns.

Basic SQL Query Structure

A simple SQL query follows this format:

This structure helps users retrieve specific data from a database based on given conditions.

History of SQL

● 1970: Dr. Edgar F. “Ted” Codd of IBM introduced the relational database model. He is known as the father of relational databases.

● 1974: Structured Query Language (SQL) appeared.

● 1978: IBM developed a prototype relational database named System/R.

● 1986: SQL was standardized by ANSI (American National Standards Institute).

Advantages of SQL

● SQL is an English-like language, making it easy to learn and understand.

● It is an ANSI standard language, approved by IT professionals and software vendors.

● SQL is platform-independent and works on different operating systems.

● It is a non-procedural language, meaning users specify what data is needed rather than how to get it.

● It supports high-performance data retrieval and manipulation.

Data and Database Concepts

● Data: A collection of raw facts such as numbers, characters, or symbols.

● Information: Processed data that has meaning.

● Database: A collection of organized data.

● DBMS (Database Management System): Software that manages databases and controls data access.

DBMS: Advantages and Disadvantages

Advantages:

● Data is well structured

● High search performance

● High data security

Disadvantages:

● Relationship between multiple tables is not supported

● Data redundancy is high

● NULL values are not supported

● To overcome these limitations, RDBMS was introduced.

RDBMS (Relational Database Management System)

RDBMS is a database management system based on the relational model introduced by Dr. E. F. Codd. In RDBMS, data is stored in multiple related tables.

Dr. E. F. Codd proposed 12 rules, known as Codd’s Rules, which define a true relational database system.

Note:

To qualify as an RDBMS, a DBMS must follow at least 6 Codd rules, including 3 mandatory rules.

Codd’s Rules (Overview)

● Information Rule (Mandatory)

● Systematic Treatment of NULL Values

● Comprehensive Data Sub-language Rule

● Non-Subversion Rule

● Rule of Guaranteed Access

● Logical Data Independence

● Physical Data Independence

● Data Distribution Rule

● Data Description Rule

● Data Integrity Rule

● View Update Rule

● High-Level Insert, Update, and Delete Rule

Mandatory Codd Rules (Must Follow)

1. Information Rule (Mandatory)

All data must be stored in tables (rows and columns).

Example: Student details must be stored in a table, not in files or pointers.

2. Systematic Treatment of NULL Values (Mandatory)

RDBMS must support NULL values.

Key Points:

● NULL ≠ 0

● NULL ≠ space

● NULL ≠ NULL

Example: If a phone number is unknown, it should be stored as NULL.

3. Rule of Guaranteed Access (Mandatory)

Each data value must be accessible using:

● Table name

● Primary key

● Column name

This avoids ambiguity and ensures direct access to data.

Important Codd Rules (Any 3 Required)

4. RDBMS must support a complete data language with:

● Data definition

● Data manipulation

● Data control

(SQL satisfies this rule.)