If you’re building a web app or working with a database, you’ve probably used joins — they help you combine data from multiple tables.
But you might wonder:
"Are joins slow or expensive?"
Let’s break it down in a simple way.
What is a Join?
A join is a way to get related data from two or more tables.
Example:
SELECT users.name, orders.total
FROM users
JOIN orders ON users.id = orders.user_id;
This gives you the user’s name along with their order total.
When Joins Are Fast
Joins work well when:
✅ You use indexes on foreign keys (like user_id)
✅ You limit the number of rows with WHERE or LIMIT
✅ You select only the fields you need
✅ You don’t join too many tables at once
Modern databases like MySQL or PostgreSQL are built to handle joins efficiently.
When Joins Can Be Slow
Joins get slow when:
❌ You don’t use indexes
❌ You join huge tables without filters
❌ You use too many nested joins
❌ You join unnecessary data (e.g., SELECT * everywhere)
Also, repeating joins in loops (N+1 problem) can make things worse, especially with ORMs.
💡 How to Keep Joins Fast
- Always index your join fields
- Use SELECT column_name, not SELECT *
- Filter your queries with WHERE
- Don’t fetch unnecessary related data
If you’re using an ORM like Prisma, it does joins smartly under the hood. Just don’t over-fetch.
Are joins expensive?
🤞 Not really — if used the right way.
They’re safe, powerful, and essential for working with relational data.
Just follow a few best practices, and you’ll be fine!
Regards,
N I Rimon