Why Doesn't My Auto-Increment ID Increase with ON DUPLICATE KEY UPDATE in MySQL?

Understanding ON DUPLICATE KEY Update with Auto Increment

Issue Description:

Inserting data into a table with an ON DUPLICATE KEY UPDATE clause results in unexpected ID increments when duplicate values are encountered. Specifically, the ID increases upon the initial insert, but remains the same upon triggering the update.

Explanation:

According to MySQL documentation, when an ON DUPLICATE KEY UPDATE clause is used, MySQL first attempts an INSERT operation. If this leads to a duplicate key value, an UPDATE operation is performed instead. However, for auto-increment columns, the increment occurs only during the INSERT operation. Therefore, even if the UPDATE operation is triggered, the auto-increment value remains the same.

Solution:

To ensure proper auto-increment increments, it is not advisable to rely on having a gapless ID sequence. Instead, consider calculating and managing incremental values manually or using the AUTO_INCREMENT function on output.

Additional Notes:

• For maintaining a gapless ID sequence, a more expensive mechanism involving table locking and renumbering is required.
• Using calculated incremental values on output can provide a more efficient and flexible solution.

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