👀 Views: 287 💬 Answers: 1 📅 Created: 2025-07-17

mysql performance indexing SQL

I'm reviewing some code and I'm following best practices but I'm maintaining legacy code that I'm sure I'm missing something obvious here, but I'm facing performance issues with a specific JOIN query in MySQL 8.0. The query is designed to retrieve user data alongside their associated orders from two tables: `users` and `orders`. Both tables have composite indexes, but I'm still experiencing slow response times, especially when the dataset grows larger. Here’s the query I'm using: ```sql SELECT u.id, u.name, o.order_date, o.total_amount FROM users u JOIN orders o ON u.id = o.user_id WHERE u.status = 'active' AND o.order_date >= '2023-01-01'; ``` The `users` table has a composite index on `(status, id)`, and the `orders` table has an index on `(user_id, order_date)`. I've run `EXPLAIN` on the query and it shows that the full scan for the `orders` table is being performed, which is unexpected given the index. Here’s the output of the `EXPLAIN`: ```plaintext +----+-------------+-------+------+---------------+---------+---------+------+------+---------------------------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+------+---------------+---------+---------+------+------+---------------------------------+ | 1 | SIMPLE | u | ALL | NULL | NULL | NULL | NULL | 1000 | Using where | | 1 | SIMPLE | o | ALL | NULL | NULL | NULL | NULL | 5000 | Using where; Using join buffer | +----+-------------+-------+------+---------------+---------+---------+------+------+---------------------------------+ ``` I’ve tried using `STRAIGHT_JOIN`, but that didn’t help. Additionally, I considered modifying the index in the `orders` table to have `(order_date, user_id)`, but I’m unsure how much this would impact other queries. What steps can I take to optimize this JOIN further? Any best practices for indexing in such scenarios would be greatly appreciated. My development environment is Linux. This is happening in both development and production on Ubuntu 22.04. I appreciate any insights! I'm developing on macOS with Sql. The stack includes Sql and several other technologies. Is this even possible? I'm coming from a different tech stack and learning Sql. Any ideas what could be causing this?