Whatever autocd is, you don't tell us. From the "table definition" you posted, it seems as if userid was declared as PRIMARY KEY NOT NULL AUTOINCREMENT which should be a hint to MySQL to make this an automatic primary key. Maybe you can enable the DBI logging and look at what SQL gets sent to MySQL:

DBI->trace(99);
[download]

Update: Now, reading the title you gave to your question, I realize that you're talking about Class::DBI and thus your autocd class likely is a subclass of Class::DBI. It would then likely help to see the (Class::DBI-setup-)part of autocd too.