Unexpected row duplication when using INSERT ... ON DUPLICATE KEY UPDATE in MySQL 5.7
I'm working on a personal project and I'm working with an scenario with MySQL 5.7 where I expect my `INSERT ... ON DUPLICATE KEY UPDATE` statement to behave in a certain way, but it seems to be duplicating rows instead. Here's what my table looks like: ```sql CREATE TABLE users ( id INT PRIMARY KEY, username VARCHAR(50) UNIQUE, email VARCHAR(100) ); ``` I'm trying to insert a new user or update the existing one based on the `username`. My SQL statement looks like this: ```sql INSERT INTO users (username, email) VALUES ('johndoe', 'johndoe@example.com') ON DUPLICATE KEY UPDATE email = VALUES(email); ``` However, when I run this code multiple times with the same `username`, I end up with duplicate entries where the `id` column increments instead of updating the existing row. The behavior I receive is `Duplicate entry 'johndoe' for key 'username'`. I don't have any triggers set up that might be affecting this behavior, and I've confirmed that the `username` field is indeed unique. I've also checked the `id` field to ensure it's being auto-incremented properly. I've tried different variations, such as using `REPLACE INTO` instead of `INSERT`, but that just results in the same scenario. Additionally, I've ensured there are no active transactions that could be causing deadlocks or race conditions. Can someone shed some light on why this might be happening or suggest a way to troubleshoot further? This issue appeared after updating to Sql 3.11. Any examples would be super helpful.