Workaround issue #94: Using Substr with aggregate throws error

sql_server/pyodbc/base.py

@@ -479,6 +479,10 @@ def enable_constraint_checking(self):
         if not self.needs_rollback:
             self.check_constraints()
 
+import datetime
+from decimal import Decimal
+from uuid import UUID
+
 
 class CursorWrapper(object):
     """
@@ -493,6 +497,36 @@ def __init__(self, cursor, connection):
         self.last_sql = ''
         self.last_params = ()
 
+    def _pytype_to_sqltype(self, typ, value):
+        if value is None:
+            return 'INT'
+        elif isinstance(value, str):
+            length = len(value)
+            if length == 0:
+                return 'NVARCHAR'
+            return 'NVARCHAR(%s)' % len(value)
+        elif typ == int:
+            if value < 0x7FFFFFFF and value > -0x7FFFFFFF:
+                return 'INT'
+            else:
+                return 'BIGINT'
+        elif typ == float:
+            return 'FLOAT'
+        elif typ == bool:
+            return 'BIT'
+        elif isinstance(value, Decimal):
+            return 'NUMERIC'
+        elif isinstance(value, datetime.date):
+            return 'DATE'
+        elif isinstance(value, datetime.time):
+            return 'TIME'
+        elif isinstance(value, datetime.datetime):
+            return 'TIMESTAMP'
+        elif isinstance(value, UUID):
+            return 'uniqueidentifier'
+        else:
+            raise NotImplementedError('not support type %s (%s)' % (type(value), repr(value)))
+
     def close(self):
         if self.active:
             self.active = False
@@ -536,8 +570,38 @@ def format_params(self, params):
 
         return tuple(fp)
 
+    def _fix_for_params(self, query, params, unify_by_values=False):
+        if params is None:
+            params = []
+            query = query
+        elif unify_by_values and len(params) > 0:
+            # Same workaround from django/db/backends/oracle/base.py
+
+            # Handle params as a dict with unified query parameters by their
+            # values. It can be used only in single query execute() because
+            # executemany() shares the formatted query with each of the params
+            # list. e.g. for input params = [0.75, 2, 0.75, 'sth', 0.75]
+            # params_dict = {0.75: ':arg0', 2: ':arg1', 'sth': ':arg2'}
+            # args = [':arg0', ':arg1', ':arg0', ':arg2', ':arg0']
+            # params = {':arg0': 0.75, ':arg1': 2, ':arg2': 'sth'}
+            params = [(param, type(param)) for param in params]
+            params_dict = {param: '@arg%d' % i for i, param in enumerate(set(params))}
+            args = [params_dict[param] for param in params]
+
+            variables = []
+            params = []
+            for key, value in params_dict.items():
+                datatype = self._pytype_to_sqltype(key[1], key[0])
+                variables.append("%s %s = %%s " % (value, datatype))
+                params.append(key[0])
+            query = ('DECLARE %s \n' % ','.join(variables)) + (query % tuple(args))
+            params = tuple(params)
+        return query, params
+
     def execute(self, sql, params=None):
         self.last_sql = sql
+        if 'GROUP BY' in sql:
+            sql, params = self._fix_for_params(sql, params, unify_by_values=True)
         sql = self.format_sql(sql, params)
         params = self.format_params(params)
         self.last_params = params