diff -r 1001fb86d7f7 -r 123f2c0995b8 src/Pure/General/sql.scala
--- a/src/Pure/General/sql.scala	Mon May 08 15:13:40 2017 +0200
+++ b/src/Pure/General/sql.scala	Mon May 08 16:00:14 2017 +0200
@@ -48,6 +48,10 @@
     "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 */