- union(), intersect(), except() and other "compound" types

of statements have more consistent behavior w.r.t.
parenthesizing.   Each compound element embedded within
another will now be grouped with parenthesis - previously,
the first compound element in the list would not be grouped,
as SQLite doesn't like a statement to start with
parenthesis.   However, Postgresql in particular has
precedence rules regarding INTERSECT, and it is
more consistent for parenthesis to be applied equally
to all sub-elements.   So now, the workaround for SQLite
is also what the workaround for PG was previously -
when nesting compound elements, the first one usually needs
".alias().select()" called on it to wrap it inside
of a subquery.  [ticket:1665]

1 files changed, 1 insertions, 5 deletions

diff --git a/lib/sqlalchemy/sql/expression.py b/lib/sqlalchemy/sql/expression.py
index eb64fd571..cf5d98d8f 100644
--- a/lib/sqlalchemy/sql/expression.py
+++ b/lib/sqlalchemy/sql/expression.py
@@ -3362,11 +3362,7 @@ class CompoundSelect(_SelectBaseMixin, FromClause):
                         (1, len(self.selects[0].c), n+1, len(s.c))
                 )
 
-            # unions group from left to right, so don't group first select
-            if n:
-                self.selects.append(s.self_group(self))
-            else:
-                self.selects.append(s)
+            self.selects.append(s.self_group(self))
 
         _SelectBaseMixin.__init__(self, **kwargs)