added outer join support...michael was right :)

And once again, thanks to Michael Bayer for forging the way on this one.
The Oracle dialect code was still pretty much copied directly over.

sqlbase7_sa/sqlbase7.py

@@ -26,6 +26,7 @@
 from sqlalchemy.engine.default import DefaultDialect
 from sqlalchemy import types, and_
 from sqlalchemy.sql.expression import Join
+from sqlalchemy.sql import visitors, operators, ClauseElement
 
 
 import sqlalchemy
@@ -56,7 +57,12 @@ class SQLBase7Compiler(CompilerBase):
         return self.process(join.left, **kwargs) + ", " + self.process(join.right, **kwargs)
 
     def visit_select(self, select, **kwargs):
-        froms = select._get_display_froms()
+        if self.stack and 'from' in self.stack[-1]:
+            existingfroms = self.stack[-1]['from']
+        else:
+            existingfroms = None
+            
+        froms = select._get_display_froms(existingfroms)
         whereclause = self._get_join_whereclause(froms)
         if whereclause is not None:
             select = select.where(whereclause)
@@ -71,7 +77,16 @@ class SQLBase7Compiler(CompilerBase):
         clauses = []
 
         def visit_join(join):
-            clauses.append(join.onclause)
+            if join.isouter:
+                def visit_binary(binary):
+                    if binary.operator == operators.eq:
+                        if binary.left.table is join.right:
+                            binary.left = _OuterJoinColumn(binary.left)
+                        elif binary.right.table is join.right:
+                            binary.right = _OuterJoinColumn(binary.right)
+                clauses.append(visitors.cloned_traverse(join.onclause, {}, {'binary':visit_binary}))
+            else:
+                clauses.append(join.onclause)
             for j in join.left, join.right:
                 if isinstance(j, Join):
                     visit_join(j)
@@ -84,6 +99,16 @@ class SQLBase7Compiler(CompilerBase):
             return and_(*clauses)
         return None
 
+    def visit_outer_join_column(self, vc):
+        return self.process(vc.column) + "(+)"
+
+
+class _OuterJoinColumn(ClauseElement):
+    __visit_name__ = 'outer_join_column'
+    
+    def __init__(self, column):
+        self.column = column
+
 
 class SQLBase7Dialect(DefaultDialect):