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

SELECT

Choose the columns you need.

Select columns

SELECT user_id, country, created_at
FROM users;

WHERE

Filter rows.

Filter by country

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

Common operators

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

Multiple filters

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

ORDER BY

Sort newest users

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

LIMIT

Limits are great for exploration.

Inspect sample rows

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.

diagram Query execution order mermaid

  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"]

SQL runs FROM/WHERE first, then picks columns, and sorts/limits last — not top-to-bottom as written.

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.

Analyst’s tip

Read a query in this order — FROM → WHERE → SELECT → ORDER BY → LIMIT — whenever the result looks wrong. Most “why is my filter not working” bugs come from expecting SQL to run in written order instead of execution order.

🧪 Try It Yourself

Exercise 1 – SELECT specific columns

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Exercise 2 – WHERE with multiple conditions

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Exercise 3 – ORDER BY and LIMIT together

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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.