Unexpected Duplicate Rows When Using INSERT IGNORE with a Unique Constraint in MySQL 5.7
I'm facing an issue where, despite using `INSERT IGNORE` with a unique constraint, I'm still ending up with duplicate rows in my table. My table is defined as follows: ```sql CREATE TABLE users ( id INT AUTO_INCREMENT PRIMARY KEY, email VARCHAR(255) UNIQUE, created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP ); ``` I'm inserting records like this: ```sql INSERT IGNORE INTO users (email) VALUES ('test@example.com'); ``` When I run this insert statement multiple times for the same email, I expect MySQL to ignore the duplicates due to the unique constraint on the email column. However, I am seeing unexpected behavior where, under certain circumstances, I still get duplicate rows. For instance, when multiple requests attempt to insert the same email at nearly the same time, it seems that some records are being inserted before the duplicate check occurs. To mitigate this, I've tried wrapping my insert statements in a transaction: ```sql START TRANSACTION; INSERT IGNORE INTO users (email) VALUES ('test@example.com'); COMMIT; ``` However, this doesn't resolve the issue. Additionally, I checked MySQL's isolation level, which is set to `REPEATABLE READ`. I'm concerned that this might be affecting the behavior. I also tried changing my insert statement to use `INSERT ... ON DUPLICATE KEY UPDATE`, but that leads to the same issue with the duplicate insertion. What steps can I take to ensure that my unique constraint is respected and to handle concurrent inserts correctly? Are there specific configurations or patterns in MySQL 5.7 that I should be aware of to prevent this? Any insights or suggestions would be greatly appreciated.