1 files changed, 118 insertions, 0 deletions
diff --git a/django/db/models/functions/window.py b/django/db/models/functions/window.py
new file mode 100644
index 0000000000..3719dfca88
--- /dev/null
+++ b/django/db/models/functions/window.py
@@ -0,0 +1,118 @@
+from django.db.models import FloatField, Func, IntegerField
+
+__all__ = [
+    'CumeDist', 'DenseRank', 'FirstValue', 'Lag', 'LastValue', 'Lead',
+    'NthValue', 'Ntile', 'PercentRank', 'Rank', 'RowNumber',
+]
+
+
+class CumeDist(Func):
+    function = 'CUME_DIST'
+    name = 'CumeDist'
+    output_field = FloatField()
+    window_compatible = True
+
+
+class DenseRank(Func):
+    function = 'DENSE_RANK'
+    name = 'DenseRank'
+    output_field = IntegerField()
+    window_compatible = True
+
+
+class FirstValue(Func):
+    arity = 1
+    function = 'FIRST_VALUE'
+    name = 'FirstValue'
+    window_compatible = True
+
+
+class LagLeadFunction(Func):
+    window_compatible = True
+
+    def __init__(self, expression, offset=1, default=None, **extra):
+        if expression is None:
+            raise ValueError(
+                '%s requires a non-null source expression.' %
+                self.__class__.__name__
+            )
+        if offset is None or offset <= 0:
+            raise ValueError(
+                '%s requires a positive integer for the offset.' %
+                self.__class__.__name__
+            )
+        args = (expression, offset)
+        if default is not None:
+            args += (default,)
+        super().__init__(*args, **extra)
+
+    def _resolve_output_field(self):
+        sources = self.get_source_expressions()
+        return sources[0].output_field
+
+
+class Lag(LagLeadFunction):
+    function = 'LAG'
+    name = 'Lag'
+
+
+class LastValue(Func):
+    arity = 1
+    function = 'LAST_VALUE'
+    name = 'LastValue'
+    window_compatible = True
+
+
+class Lead(LagLeadFunction):
+    function = 'LEAD'
+    name = 'Lead'
+
+
+class NthValue(Func):
+    function = 'NTH_VALUE'
+    name = 'NthValue'
+    window_compatible = True
+
+    def __init__(self, expression, nth=1, **extra):
+        if expression is None:
+            raise ValueError('%s requires a non-null source expression.' % self.__class__.__name__)
+        if nth is None or nth <= 0:
+            raise ValueError('%s requires a positive integer as for nth.' % self.__class__.__name__)
+        super().__init__(expression, nth, **extra)
+
+    def _resolve_output_field(self):
+        sources = self.get_source_expressions()
+        return sources[0].output_field
+
+
+class Ntile(Func):
+    function = 'NTILE'
+    name = 'Ntile'
+    output_field = IntegerField()
+    window_compatible = True
+
+    def __init__(self, num_buckets=1, **extra):
+        if num_buckets <= 0:
+            raise ValueError('num_buckets must be greater than 0.')
+        super().__init__(num_buckets, **extra)
+
+
+class PercentRank(Func):
+    function = 'PERCENT_RANK'
+    name = 'PercentRank'
+    output_field = FloatField()
+    window_compatible = True
+
+
+class Rank(Func):
+    function = 'RANK'
+    name = 'Rank'
+    output_field = IntegerField()
+    window_compatible = True
+
+
+class RowNumber(Func):
+    function = 'ROW_NUMBER'
+    name = 'RowNumber'
+    output_field = IntegerField()
+    window_compatible = True