id        int      NOT NULL auto_increment,
     useragent char(32) NOT NULL,
     ip        char(32) NOT NULL,
     date      char(32) NOT NULL,
     useragent char(32),              -- added field for ua
     primary key  (id)

##</code><code>##

     ...
     countdown  int  default(0),
     ...

##</code><code>##

    UPDATE Table set countdown = countdown + 1 where useragent = ?;

    DELETE FROM Table WHERE countdown > 10;