MySQL 5.7: INDEX_MERGE optimization strategy scenarios with complex WHERE clause
I'm following best practices but I'm having a hard time understanding I'm working on a project and hit a roadblock... I'm stuck on something that should probably be simple... After trying multiple solutions online, I still can't figure this out. I'm working with a performance scenario with a complex query in MySQL 5.7 that involves an `INDEX_MERGE` strategy. The query is taking significantly longer to execute than expected, even with appropriate indexes in place. The query looks something like this: ```sql SELECT * FROM orders WHERE status = 'completed' AND (customer_id IN (SELECT id FROM customers WHERE region = 'North America') OR order_date > '2023-01-01'); ``` The table `orders` has an index on `status` and `order_date`, and the table `customers` has an index on `region`. I initially expected MySQL to utilize the indexes effectively, especially given the use of the `IN` clause and the logical `OR`, but the performance has been subpar. I've tried running `EXPLAIN` on this query, and it shows that MySQL is choosing to use the `INDEX_MERGE` strategy, but it seems to be performing a full table scan on `orders`. Here's what the `EXPLAIN` output looks like: ```plaintext +----+-------------+--------+------+---------------+---------+---------+------+------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+--------+------+---------------+---------+---------+------+------+-------------+ | 1 | SIMPLE | orders | ALL | NULL | NULL | NULL | NULL | 10000 | Using where | +----+-------------+--------+------+---------------+---------+---------+------+------+-------------+ ``` I tried breaking down the query by running each condition separately to see the execution time individually. The customer subquery runs quickly by itself, and the filtering by status also performs well, but combined, it’s as if MySQL fails to optimize correctly. I’ve considered restructuring the query to use a `UNION`, but I’m not sure if that would help. Is there a better approach to optimize such queries in MySQL 5.7? Are there specific configurations or patterns that I might be overlooking to help MySQL handle this more efficiently? This is part of a larger API I'm building. What's the best practice here? Thanks for your help in advance! This is happening in both development and production on Windows 11. I'm on Linux using the latest version of Sql. Could this be a known issue? Has anyone dealt with something similar?