Fixed #10906 -- Added a check for PostgreSQL pre 8.2 when using StdDev/Variance aggregates. Thanks to Richard Davies for the report and patch.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@10731 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/db/backends/postgresql/operations.py

@@ -146,11 +146,18 @@ class DatabaseOperations(BaseDatabaseOperations):
     def check_aggregate_support(self, aggregate):
         """Check that the backend fully supports the provided aggregate.
 
+        The population and sample statistics (STDDEV_POP, STDDEV_SAMP,
+        VAR_POP, VAR_SAMP) were first implemented in Postgres 8.2.
+
         The implementation of population statistics (STDDEV_POP and VAR_POP)
         under Postgres 8.2 - 8.2.4 is known to be faulty. Raise
         NotImplementedError if this is the database in use.
         """
-        if aggregate.sql_function == 'STDDEV_POP' or aggregate.sql_function == 'VAR_POP':
+        if aggregate.sql_function in ('STDDEV_POP', 'STDDEV_SAMP', 'VAR_POP', 'VAR_SAMP'):
+            if self.postgres_version[0:2] < [8,2]:
+                raise NotImplementedError('PostgreSQL does not support %s prior to version 8.2. Please upgrade your version of PostgreSQL.' % aggregate.sql_function)
+
+        if aggregate.sql_function in ('STDDEV_POP', 'VAR_POP'):
             if self.postgres_version[0:2] == [8,2]:
                 if self.postgres_version[2] is None or self.postgres_version[2] <= 4:
                     raise NotImplementedError('PostgreSQL 8.2 to 8.2.4 is known to have a faulty implementation of %s. Please upgrade your version of PostgreSQL.' % aggregate.sql_function)

tests/regressiontests/aggregation_regress/models.py

@@ -1,7 +1,7 @@
 # coding: utf-8
 import pickle
 
-from django.db import models
+from django.db import connection, models
 from django.conf import settings
 
 try:
@@ -321,10 +321,26 @@ FieldError: Cannot compute Avg('mean_age'): 'mean_age' is an aggregate
 """
 }
 
-if settings.DATABASE_ENGINE != 'sqlite3':
-    __test__['API_TESTS'] += """
-# Stddev and Variance are not guaranteed to be available for SQLite.
+def run_stddev_tests():
+    """Check to see if StdDev/Variance tests should be run.
 
+    Stddev and Variance are not guaranteed to be available for SQLite, and
+    are not available for PostgreSQL before 8.2.
+    """
+    if settings.DATABASE_ENGINE == 'sqlite3':
+        return False
+
+    class StdDevPop(object):
+        sql_function = 'STDDEV_POP'
+
+    try:
+        connection.ops.check_aggregate_support(StdDevPop())
+    except:
+        return False
+    return True
+
+if run_stddev_tests():
+    __test__['API_TESTS'] += """
 >>> Book.objects.aggregate(StdDev('pages'))
 {'pages__stddev': 311.46...}