[Dbix-class] Comparing two columns in a table

[Matija Grabnar]

Say that I have a table which contains, among other stuff, two columns
(call them a and b):

I want to select only those rows where the two columns are unequal.

select * from sometable where sometable.a != sometable.b;

I've looked through Dbix::Class::Resultset and Cookbook, as well as 
SQL::Abstract man page, and couldn't find anything that showed
how to compare two columns in the same table, only how to use a function 
on a column.

Any ideas?