293,305d292
<     def visit_select_precolumns(self, select):
<         if select.distinct:
<             if type(select.distinct) == bool:
<                 return "DISTINCT "
<             if type(select.distinct) == list:
<                 dist_set = "DISTINCT ON ("
<                 for col in select.distinct:
<                     dist_set += str(col) + ", "
<                 dist_set = dist_set[:-2] + ") "
<                 return dist_set
<             return "DISTINCT ON (" + str(select.distinct) + ") "
<         else:
<             return ""