src/Pure/General/sql.scala

   def enclosure(ss: Iterable[Source]): Source = ss.mkString("(", ", ", ")")
 
   def select(columns: List[Column] = Nil, distinct: Boolean = false): Source =
     "SELECT " + (if (distinct) "DISTINCT " else "") +
     (if (columns.isEmpty) "*" else commas(columns.map(_.ident))) + " FROM "
+
+  val join_outer: Source = " LEFT OUTER JOIN "
+  val join_inner: Source = " INNER JOIN "
+  def join(outer: Boolean = false): Source = if (outer) join_outer else join_inner
 
 
   /* types */
 
   object Type extends Enumeration