2. SELECT basics — reading rows
SQL · 48 pages source format
Every query starts with SELECT. Name columns explicitly in production. DISTINCT removes duplicates. Aliases rename columns or tables.
What you'll learn
- SELECT columns
- DISTINCT
- Column aliases
- FROM and table names
Basic SELECT
SELECT col1, col2 FROM table. Avoid SELECT * in production — it hides schema changes and fetches unnecessary data.
SELECT id, name, email
FROM users;Do this now
SQLBolt lesson 1. Save query as queries/01_select.sql.
DISTINCT and aliases
SELECT DISTINCT country FROM customers. SELECT total AS order_total — aliases clarify output headers.
Do this now
List unique product categories. Alias a computed column: quantity * price AS line_total.
Explore schema first
Before querying: .schema in SQLite, \d in psql, or DESCRIBE in MySQL. Know column names and types.
Do this now
Document your sandbox schema in sql-notes/SCHEMA.md — tables, keys, sample row counts.
Pro tip. QA tip: schema docs become test oracle references.