code: function(table) {
      return table.getEffectiveName() ==
          joinStep.predicate.rightColumn.getTable().getEffectiveName() ?
              joinStep.predicate.rightColumn : joinStep.predicate.leftColumn;
    }
docs: Finds which of the two joined columns corresponds to the given table.
  @param {!lf.schema.Table} table
  @return {!lf.schema.Column}