MySQL 5.7 - Slow Query Performance with JOINs and Large Data Sets
I'm a bit lost with I've been banging my head against this for hours... I tried several approaches but none seem to work. I've been experiencing significant performance issues when running queries that involve joins across multiple large tables in MySQL 5.7. The specific query I'm using looks like this: ```sql SELECT a.id, a.name, b.amount, c.date FROM table_a AS a JOIN table_b AS b ON a.id = b.a_id JOIN table_c AS c ON b.id = c.b_id WHERE c.date >= '2023-01-01' AND c.date <= '2023-12-31'; ``` The tables involved have millions of rows, and I've indexed the foreign keys `a_id` in `table_b` and `b_id` in `table_c`, but the query still takes over 30 seconds to execute. When I run `EXPLAIN` on this query, it shows a large number of rows being scanned. Here’s the output: ```plaintext +----+-------------+-------+------+---------------+---------+---------+---------------------+------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+------+---------------+---------+---------+---------------------+------+-------------+ | 1 | SIMPLE | a | ALL | NULL | NULL | NULL | NULL | 5000 | | | 1 | SIMPLE | b | ref | a_id | a_id | 4 | mydb.a.id | 200 | Using index | | 1 | SIMPLE | c | ref | b_id | b_id | 4 | mydb.b.id | 1000 | Using where | +----+-------------+-------+------+---------------+---------+---------+---------------------+------+-------------+ ``` From this, it looks like `table_a` is doing a full table scan, which seems to be the bottleneck. I’ve tried optimizing the query by explicitly selecting only the necessary fields and ensured the foreign keys are indexed. However, performance hasn't improved significantly. I also considered using partitioning, but I'm unsure if it's the right approach for these specific tables. Does anyone have suggestions for optimizing this query further or alternative approaches to improve its performance? Any insights on whether restructuring the database or query could help would be greatly appreciated! My development environment is Linux. Thanks in advance! I'm on Ubuntu 22.04 using the latest version of Sql. What's the correct way to implement this? This is for a microservice running on CentOS.