How to prevent RMySQL warnings "Unsigned INTEGER in col imported as numeric"?

You're not doing anything incorrectly--RMySQL "helpfully" gives you all those warnings just in case that wasn't what you want (it almost always is). @hadley recommends installing the development version (0.11.x) in which this annoyance is reportedly solved. Otherwise, you can use suppressWarnings(...), where ... is the statement for which you want to hide warnings. Or just live with it till version 0.11 hits CRAN.

Switching from RMySQL to RMariaDB also removes the warnings, see https://github.com/r-dbi/RMySQL/issues/37.