Ignored columns are produced when aliasing a column. For example,
aliasing "catalog.reference" as "reference".
Before this change, this would cause conditions on "reference" to be
rendered non-mapped, which can cause SQL execution issues when there is
more than one "reference" column available (catalog.reference and its
alias counting as only one), which is the case when
catalog-category-catalog joins happen.

Instead, render all columns which could be mapped, independently from
their "ignored" status.

Also, use a different local variable for table aliases than for column
aliases.
Also, use more "return" statements, and simplify conditional structure.