Does auto increment start again at 0 if max value reached?

Question

Does MySQL's auto increment reset to 0 after reaching the maximum value?

In other words, if an UNSIGNED SMALLINT column with AUTO_INCREMENT reaches 65535 what happens on a new INSERT?

If there are no available values, what happens then?

Answer 1

The documentation is pretty clear on what happens:

When the column reaches the upper limit of the data type, the next attempt to generate a sequence number fails.

Read about it here.

So the answer to your question is "no". It generates an error.