Introduction to SQL: Database Concepts

What is a Database?

A database is a structured collection of data stored electronically. It allows efficient storage, retrieval, and management of information.

Relational databases organize data into tables, which consist of rows and columns.

• Stores data in a structured format
• Supports data retrieval and manipulation
• Enables data relationships through tables

Tables, Rows, and Columns

In a relational database, data is stored in tables. Each table represents an entity, such as Customers or Orders.

Tables consist of rows (records) and columns (fields). Each row holds data for one record, and each column represents a data attribute.

• Table: collection of related data entries
• Row: a single data record
• Column: a data attribute or field

Keys and Relationships

Keys are special columns used to identify records uniquely and establish relationships between tables.

The primary key uniquely identifies each row in a table, ensuring no duplicates.

A foreign key is a column that links to the primary key in another table, creating a relationship.

• Primary Key: unique identifier for table records
• Foreign Key: references primary key in another table
• Relationships enable joining data across tables