1 files changed, 62 insertions, 0 deletions
diff --git a/lib/sqlalchemy/sql/elements.py b/lib/sqlalchemy/sql/elements.py
index 8df22b7a6..91d081ca0 100644
--- a/lib/sqlalchemy/sql/elements.py
+++ b/lib/sqlalchemy/sql/elements.py
@@ -2892,6 +2892,68 @@ class Over(ColumnElement):
         ))
 
 
+class WithinGroup(ColumnElement):
+    """Represent an WITHIN GROUP clause.
+
+    This is a special operator against so-called ordered-set
+    and hypothetical-set aggregate functions in the SQL:2008 standard.
+    """
+    __visit_name__ = 'within_group'
+
+    order_by = None
+
+    def __init__(self, func, order_by):
+        """Produce an :class:`.WithinGroup` object against a function.
+
+        Used against ordered-set aggregates for databases that support
+        ordered-set aggregate functions
+
+        E.g.::
+
+            from sqlalchemy import within_group
+            within_group(func.percentile_disc(0.25), order_by='x')
+
+        Would produce "PERCENTILE_DISC(0.25) WITHIN GROUP (ORDER BY x)".
+
+        :param func: a :class:`.FunctionElement` construct, typically
+         generated by :data:`~.expression.func`.
+        :param order_by: a column element or string, or a list
+         of such, that will be used as the ORDER BY clause
+         of the WITHIN GROUP construct.
+
+        This function is also available from the :data:`~.expression.func`
+        construct itself via the :meth:`.FunctionElement.within_group` method.
+
+        .. versionadded:: 1.0
+
+        """
+        self.func = func
+        self.order_by = ClauseList(
+            *util.to_list(order_by),
+            _literal_as_text=_literal_as_label_reference)
+
+    @util.memoized_property
+    def type(self):
+        return self.func.type
+
+    def get_children(self, **kwargs):
+        return [c for c in
+                (self.func, self.order_by)
+                if c is not None]
+
+    def _copy_internals(self, clone=_clone, **kw):
+        self.func = clone(self.func, **kw)
+        self.order_by = clone(self.order_by, **kw)
+
+    @property
+    def _from_objects(self):
+        return list(itertools.chain(
+            *[c._from_objects for c in
+                (self.func, self.order_by)
+              if c is not None]
+        ))
+
+
 class FunctionFilter(ColumnElement):
     """Represent a function FILTER clause.