Stop Writing Slow SQL: 7 Query Optimization Tricks Every Developer Should Know

You pushed a feature last week. Everything looked fine in staging. Then production blew up. The culprit? A single SQL query that took 3 milliseconds on your laptop with 500 rows — and 14 seconds on production with 2 million rows. Sound familiar? SQL is one of those skills where the gap between "works" and "works well" is enormous. Most developers learn just enough SQL to get data in and out of a database, then wonder why their app crawls under real-world load. This guide covers 7 practical optimizations that make a measurable difference. No theory fluff — just patterns you can apply today. 1. Stop Doing SELECT * in Production Code This is the most common and most forgiven sin in SQL. It looks harmless but it has real costs: Transfers more data over the network than needed Prevents the database from using covering indexes Makes your code fragile when table schema changes Before: SELECT * FROM orders WHERE user_id = 42 ; After: SELECT id , status , total_amount , created_at FROM orders W