Vista Academy · SQL Data Analytics · Lesson 2
Databases, Tables and Keys
Learn how relational data is organized, how primary and foreign keys identify and connect records, and how to model a customer-order relationship.
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Concept 1 of 8
A Database Is a Collection of Tables
A database stores related information in an organized way. A customer database might contain Customers, Orders and Products tables, each holding a different kind of information.
- A database can contain multiple tables.
- Each table represents a subject or entity.
- Tables can be connected through related columns.
Step 1 · Interactive teaching lab
A Database Is a Collection of Tables
Select a table to inspect the type of information it stores.
| customer_id | name | city |
|---|---|---|
| 101 | Rahul | Delhi |
| 102 | Priya | Mumbai |
| 103 | Amit | Pune |
| 104 | Neha | Delhi |
Customers stores customer identity and profile details.
Step 2 · Apply it
A shop stores customer details and order details. What is the best structure?
Lesson FAQ
Questions learners often ask
What You Will Learn in SQL Lesson 2
This lesson explains relational databases, table structure, primary keys, foreign keys, one-to-many relationships and composite keys through a small customer-orders example.
Why Keys Matter in Real Business
Keys help businesses identify records consistently and connect information across tables. A customer-order relationship makes it possible to analyse purchases without repeating all customer details on every order.
Common Beginner Mistakes
- Assuming names are always unique.
- Using a field with duplicate values as a primary key.
- Confusing a primary key with a foreign key.
- Repeating customer information unnecessarily in every order row.
Frequently Asked Questions
What is a primary key in SQL?
A primary key uniquely identifies each row in a table and cannot contain duplicate or NULL values.
What is a foreign key in SQL?
A foreign key refers to a key in another table and helps maintain valid relationships between records.
What is the difference between a primary key and a foreign key?
A primary key identifies a row in its own table. A foreign key stores a reference to a key in another table.
What is a composite key?
A composite key uses two or more columns together to uniquely identify a row.