Lesson 3: SELECT Queries

🔍 Lesson 3: SELECT Queries (Retrieving Data)

⏱️ Estimated time: 20 minutes | Difficulty: Beginner

The Foundation

The SELECT statement is used to retrieve data from a database. It is the command you will use most often in SQL.

Basic SELECT

-- Get all columns
SELECT * FROM users;

-- Get specific columns
SELECT name, email FROM users;

-- Alias columns
SELECT name AS "Full Name", age AS "Years" FROM users;

ORDER BY (Sorting)

SELECT * FROM users ORDER BY name ASC;    -- A to Z
SELECT * FROM users ORDER BY age DESC;     -- Highest first
SELECT * FROM users ORDER BY age DESC, name ASC; -- Multiple

LIMIT & OFFSET

SELECT * FROM users LIMIT 10;           -- First 10 rows
SELECT * FROM users LIMIT 10 OFFSET 20; -- Rows 21-30 (pagination)

DISTINCT (Remove Duplicates)

SELECT DISTINCT city FROM users;  -- Unique cities only

✅ Quick Quiz

❓ What does SELECT * mean?

A) Select first column B) Select all columns C) Delete all data

❓ How to sort by age highest first?

A) ORDER BY age ASC B) ORDER BY age DESC

❓ What does DISTINCT do?

A) Removes duplicate values B) Adds new rows C) Sorts results

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