SQL Fundamentals

This lesson covers the fundamentals of SQL (Structured Query Language) for the OCR A-Level Computer Science (H446) specification. SQL is the standard language for managing and querying relational databases.

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What is SQL?

SQL (Structured Query Language) is a declarative language used to:

• Query data (retrieve specific information).
• Manipulate data (insert, update, delete records).
• Define data structures (create tables, set constraints).

SQL is declarative -- you describe WHAT data you want, not HOW to get it. The database engine determines the most efficient way to execute the query.

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SELECT Queries

The SELECT statement retrieves data from one or more tables.

Basic Syntax

SELECT column1, column2
FROM table_name
WHERE condition
ORDER BY column ASC|DESC;

Examples

-- Select all columns from Students
SELECT * FROM Students;

-- Select specific columns
SELECT Name, Age FROM Students;

-- Select with a condition
SELECT Name, Grade FROM Students WHERE Grade = 'A';

-- Select with multiple conditions
SELECT Name, Age FROM Students WHERE Age >= 16 AND Grade = 'A';

-- Select with OR
SELECT Name FROM Students WHERE Subject = 'Maths' OR Subject = 'Science';

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