MySQL 8.0: Performance Issues with Group By and Having Clause in Complex Queries
I'm trying to figure out I'm working through a tutorial and I need help solving I'm dealing with I'm currently facing performance issues with a complex query that involves multiple joins and a `GROUP BY` clause along with a `HAVING` filter... The query is intended to aggregate data from several tables, but the execution time is significantly longer than expected. Here's a simplified version of my query: ```sql SELECT u.id, COUNT(o.id) as order_count FROM users u JOIN orders o ON u.id = o.user_id JOIN order_details od ON o.id = od.order_id WHERE u.status = 'active' GROUP BY u.id HAVING order_count > 5; ``` When I run this query, it takes over 30 seconds to execute, even with a relatively small dataset of around 10,000 records in each table. I've tried indexing the `user_id` in the `orders` table and `order_id` in the `order_details` table, but the performance hasn't improved much. I also tried breaking the query into smaller parts, executing them individually, and caching the results, but that approach added unnecessary complexity to the application. Additionally, I've checked the execution plan using `EXPLAIN` and it shows a full table scan on the `users` table, which seems to be the bottleneck. Here’s the output from `EXPLAIN`: ```plaintext id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra ---|--------------|-------|------|----------------|-----|---------|-----|------|--------------------- 1 | SIMPLE | u | ALL | NULL | NULL| NULL | NULL| 10000| Using temporary; Using filesort ``` I’m running MySQL 8.0.26 and would appreciate any advice on optimizing this query or general tips on how to work with `GROUP BY` and `HAVING` in a performance-efficient way. Any insights would be extremely helpful! Has anyone dealt with something similar? The stack includes Sql and several other technologies. Has anyone dealt with something similar? Has anyone else encountered this?