SQL Basics (SELECT, WHERE, ORDER BY, LIMIT)

SELECT

Choose the columns you need.

SELECT user_id, country, created_at
FROM users;

WHERE

Filter rows.

SELECT user_id, country
FROM users
WHERE country = 'IN';

Common operators

• =, !=, >, <, >=, <=
• IN (...)
• BETWEEN a AND b
• LIKE '%text%'
• IS NULL / IS NOT NULL

SELECT user_id, created_at, plan
FROM users
WHERE country IN ('IN', 'US')
  AND plan != 'free'
  AND created_at >= '2025-01-01';

ORDER BY

SELECT user_id, created_at
FROM users
ORDER BY created_at DESC
LIMIT 20;

LIMIT

Limits are great for exploration.

SELECT *
FROM orders
LIMIT 50;

The order SQL actually runs in

This trips up almost every beginner: SQL is not executed top-to-bottom in the order you type it. The database picks the table first, filters rows, then figures out which columns to show, and sorts/limits last.

  flowchart TD
  A["FROM users"] --> B["WHERE country = 'IN'"]
  B --> C["SELECT user_id, country"]
  C --> D["ORDER BY created_at DESC"]
  D --> E["LIMIT 20"]

That's why you can filter on a column in WHERE that you never mention in SELECT — the engine already resolved WHERE against the full table before it trimmed the column list.

Check your understanding

🧪 Try It Yourself

Exercise 1 – SELECT specific columns

Press Run to see what your code prints.

Exercise 2 – WHERE with multiple conditions

Press Run to see what your code prints.

Exercise 3 – ORDER BY and LIMIT together

Press Run to see what your code prints.

Next

Once you're comfortable filtering and sorting single tables, move on to Aggregations (COUNT, SUM, AVG) and GROUP BY to start computing metrics instead of just listing rows.