A database is a collection of information or data organized in a way that it can be easily accessed, managed, and updated. For example, a school database can store student details like names, roll numbers, marks, etc.
Why Do We Need Databases?
To store data systematically.
To retrieve or update data quickly.
To avoid data duplication or mistakes.
What is a Database Management System (DBMS)?
A DBMS is software used to manage databases. It helps users create, store, and retrieve data easily.
Examples: MySQL, Oracle, and Microsoft SQL Server.
2. Relational Data Model
A relational database organizes data into tables, where each table is called a relation.
Key Terms:
Domain: A set of allowed values for a column. For example, the “Grade” column in a table may allow values like A, B, C, etc.
Tuple: A row in a table. Each row stores information about one entry.
Relation: A table in the database.
Candidate Key: A column (or a set of columns) that can uniquely identify a row in a table.
Primary Key: A column selected as the unique identifier for the table. For example, the “Roll Number” column can be a primary key.
Alternate Key: Other columns that can also act as a candidate key but are not selected as the primary key.
3. Advantages of SQL (Structured Query Language)
SQL is used to manage and interact with databases.
Benefits:
Easy to use and learn.
Allows fast data retrieval and updates.
Helps maintain large datasets efficiently.
Works with different database systems like MySQL, PostgreSQL, etc.
4. Categories of SQL
Data Definition Language (DDL):
Used to define the structure of a database.
Commands:
CREATE: To create a database or table.
DROP: To delete a database or table.
ALTER: To modify the structure of a table.
Data Manipulation Language (DML):
Used to retrieve data from a database.
Commands:
SELECT: To retrieve specific data from a table.
Used to change or manipulate data in a database.
Commands:
INSERT: To add new data.
UPDATE: To modify existing data.
DELETE: To remove data from a table.
5. Introduction to MySQL
What is MySQL? MySQL is an open-source database management system that uses SQL to manage and query data.
Steps to Use MySQL:
Install MySQL software.
Use commands to create and manage databases.
Data Types in MySQL:
INT: To store numbers.
VARCHAR: To store text data.
DATE: To store dates.
6. Common SQL Commands
Data Definition (DDL):
CREATE DATABASE: To create a new database. Example: CREATE DATABASE School;
CREATE TABLE: To create a table with specific columns. Example:sqlCopy codeCREATE TABLE Students ( RollNo INT, Name VARCHAR(50), Class INT );
DROP: To delete a database or table. Example: DROP TABLE Students;
ALTER: To modify a table. Example: ALTER TABLE Students ADD Marks INT;
Data Manipulation (DML):
SELECT: To retrieve data. Example: SELECT * FROM Students;
WHERE: To filter data based on conditions. Example: SELECT * FROM Students WHERE Class = 10;
