MySQL: Query performance issues with complex JOINs on large tables using indexes
I'm relatively new to this, so bear with me. I can't seem to get I'm working through a tutorial and I'm working on a personal project and This might be a silly question, but After trying multiple solutions online, I still can't figure this out..... I'm experiencing significant performance issues with a query that involves multiple JOINs on large tables in MySQL 8.0. The query is supposed to retrieve user activity logs joined with user details and activity types, but it takes excessively long to execute, sometimes up to several minutes. Here’s the SQL query: ```sql SELECT ua.user_id, u.name, a.activity_type, COUNT(*) as activity_count FROM user_activity ua JOIN users u ON ua.user_id = u.id JOIN activities a ON ua.activity_id = a.id WHERE ua.activity_date BETWEEN '2023-01-01' AND '2023-12-31' GROUP BY ua.user_id, u.name, a.activity_type ORDER BY activity_count DESC; ``` The `user_activity` table has about 1 million rows, `users` has around 500k rows, and `activities` has 200k rows. I’ve indexed the `user_id` and `activity_id` columns in the `user_activity` table, but the query still runs slowly. I also tried running `ANALYZE TABLE` on all relevant tables to make sure MySQL has up-to-date statistics, and I used the `EXPLAIN` command to analyze the query plan: ```sql EXPLAIN SELECT ua.user_id, u.name, a.activity_type, COUNT(*) as activity_count FROM user_activity ua JOIN users u ON ua.user_id = u.id JOIN activities a ON ua.activity_id = a.id WHERE ua.activity_date BETWEEN '2023-01-01' AND '2023-12-31' GROUP BY ua.user_id, u.name, a.activity_type ORDER BY activity_count DESC; ``` The output shows that MySQL is performing a full table scan on `user_activity`, which I believe is the root cause of the slowdown. I also checked that the indexes on `user_id` and `activity_id` are being used, but it seems that the date filter isn't effectively leveraging them. I've considered changing the date filter to an indexed column or adding a composite index on `(activity_date, user_id, activity_id)`, but I'm unsure if that would provide the desired performance improvement. What strategies can I implement to optimize this query? Are there specific indexing strategies or query rewriting techniques that can help improve the performance? I'm working on a service that needs to handle this. What's the best practice here? For context: I'm using Sql on Ubuntu. How would you solve this? My development environment is Ubuntu 22.04. Thanks in advance! This is part of a larger REST API I'm building. Is there a better approach?