C<select> as normal. (You may also use the C<cols> attribute, as in
earlier versions of DBIC.)
+Essentially C<columns> does the same as L</select> and L</as>.
+
+ columns => [ 'foo', { bar => 'baz' } ]
+
+is the same as
+
+ select => [qw/foo baz/],
+ as => [qw/foo bar/]
+
=head2 +columns
=over 4