MySQL 8.0 - Issues with EXPLAIN Output Showing Unexpected Join Order
I'm sure I'm missing something obvious here, but I'm encountering an unexpected behavior when using the `EXPLAIN` statement for a complex query in MySQL 8.0. Specifically, I'm trying to optimize a query that involves multiple inner joins across several tables, but the join order output in the `EXPLAIN` plan doesn't match my expectations based on the table sizes and indexes. Here's the query I'm working with: ```sql SELECT a.id, b.value, c.description FROM table_a AS a JOIN table_b AS b ON a.b_id = b.id JOIN table_c AS c ON b.c_id = c.id WHERE a.status = 'active' ORDER BY b.value DESC; ``` In my schema, `table_a` has about 1 million rows, `table_b` has 100,000 rows, and `table_c` has 10,000 rows. Each of these tables has appropriate indexes on the join columns. However, when I run the `EXPLAIN` command, it shows that it plans to join `table_c` first, then `table_b`, and finally `table_a`, which seems counterintuitive given the row counts. ```sql EXPLAIN SELECT a.id, b.value, c.description FROM table_a AS a JOIN table_b AS b ON a.b_id = b.id JOIN table_c AS c ON b.c_id = c.id WHERE a.status = 'active' ORDER BY b.value DESC; ``` The output indicates that the join order is `table_c`, `table_b`, and then `table_a`, which leads to a performance hit since MySQL has to read through more rows than necessary before filtering down to the final results. I've tried forcing the join order using the `STRAIGHT_JOIN` keyword, but that only made the situation worse. I've also checked the statistics on my tables and updated them with `ANALYZE TABLE`, but it doesn't seem to change the behavior. Is there any way I can influence the join order or diagnose why MySQL is making this decision? What strategies can I employ to encourage better join optimization in this case? This is part of a larger application I'm building. How would you solve this? Has anyone dealt with something similar?