Why should you care?

Backend and data jobs require SQL. Query Planner appears in interviews and daily work.

See it live — copy this example

Run in pgAdmin or psql.

-- Query Planner
SELECT id, name, email
FROM users
WHERE is_active = 1
ORDER BY name;

Run Example »

Run this SQL in your database tool (SSMS, pgAdmin, MySQL Workbench) or use the Try code button on the block above.

What happened?

• The example shows Query Planner in action.
• Read each line, then edit one part and run again.

Try it yourself

1. Open SSMS, pgAdmin, or MySQL Workbench.
2. Paste the query and run it.
3. Change the WHERE clause and see different rows.
4. Change one value in the example and run it again.
5. Break the code on purpose and read the error message.

Remember

You saw how Query Planner works. Practice by editing the example. Use Next when you can explain it in your own words.