1 files changed, 30 insertions, 6 deletions
diff --git a/lib/arel/engines/sql/primitives.rb b/lib/arel/engines/sql/primitives.rb
index 5544d63710..c4968558a2 100644
--- a/lib/arel/engines/sql/primitives.rb
+++ b/lib/arel/engines/sql/primitives.rb
@@ -13,12 +13,6 @@ module Arel
     end
   end
 
-  class Expression < Attribute
-    def to_sql(formatter = Sql::SelectClause.new(relation))
-      formatter.expression self
-    end
-  end
-
   class Value
     def to_sql(formatter = Sql::WhereCondition.new(relation))
       formatter.value value
@@ -28,4 +22,34 @@ module Arel
       object.to_sql(Sql::Value.new(relation))
     end
   end
+  
+  class Expression < Attribute
+    def to_sql(formatter = Sql::SelectClause.new(relation))
+      formatter.expression self
+    end
+  end
+  
+  class Count < Expression
+    def function_sql; 'COUNT' end
+  end
+  
+  class Distinct < Expression
+    def function_sql; 'DISTINCT' end
+  end
+  
+  class Sum < Expression
+    def function_sql; 'SUM' end
+  end
+  
+  class Maximum < Expression
+    def function_sql; 'MAX' end
+  end
+  
+  class Minimum < Expression
+    def function_sql; 'MIN' end
+  end
+  
+  class Average < Expression
+    def function_sql; 'AVG' end
+  end
 end
 \ No newline at end of file