MySQL 5.7: Slow performance on SELECT with GROUP BY and HAVING clauses on large dataset
I've tried everything I can think of but I'm currently facing performance issues with a SELECT query that uses GROUP BY and HAVING clauses on a large dataset in MySQL 5.7. The query looks like this: ```sql SELECT user_id, COUNT(*) as order_count FROM orders WHERE order_date >= '2023-01-01' GROUP BY user_id HAVING COUNT(*) > 5; ``` The `orders` table contains over a million rows, and this query takes several seconds to execute. I've indexed `user_id` and `order_date`, but I'm still seeing high execution times. I tried running the query with `EXPLAIN` and got the following output: ``` +----+-------------+-------+------+---------------+---------+---------+------+---------+----------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+------+---------------+---------+---------+------+---------+----------+-------------+ | 1 | SIMPLE | orders | ALL | user_id,order_date | NULL | NULL | NULL | 1000000 | Using where; Using temporary; Using filesort | +----+-------------+-------+------+---------------+---------+---------+------+---------+----------+-------------+ ``` The `Using temporary; Using filesort` in the `Extra` column suggests that I might be facing issues with sorting or temporary tables. I've tried optimizing the query by changing the order of operations, but that didn't seem to help. Additionally, I've considered using a subquery to filter out users with more than five orders before grouping, like this: ```sql SELECT user_id, order_count FROM ( SELECT user_id, COUNT(*) as order_count FROM orders WHERE order_date >= '2023-01-01' GROUP BY user_id ) as subquery WHERE order_count > 5; ``` However, this new query also takes a long time to run. Do you have any recommendations on how to improve the performance of this query? Are there specific indexing strategies I should consider or alternative query structures that might yield better results?