Index: app/models/issue_query.rb
===================================================================
--- app/models/issue_query.rb	(revision 15109)
+++ app/models/issue_query.rb	(working copy)
@@ -32,8 +32,8 @@
     QueryColumn.new(:updated_on, :sortable => "#{Issue.table_name}.updated_on", :default_order => 'desc'),
     QueryColumn.new(:category, :sortable => "#{IssueCategory.table_name}.name", :groupable => true),
     QueryColumn.new(:fixed_version, :sortable => lambda {Version.fields_for_order_statement}, :groupable => true),
-    QueryColumn.new(:start_date, :sortable => "#{Issue.table_name}.start_date"),
-    QueryColumn.new(:due_date, :sortable => "#{Issue.table_name}.due_date"),
+    QueryColumn.new(:start_date, :sortable => "#{Issue.table_name}.start_date", :groupable => true),
+    QueryColumn.new(:due_date, :sortable => "#{Issue.table_name}.due_date", :groupable => true),
     QueryColumn.new(:estimated_hours, :sortable => "#{Issue.table_name}.estimated_hours", :totalable => true),
     QueryColumn.new(:total_estimated_hours,
       :sortable => "COALESCE((SELECT SUM(estimated_hours) FROM #{Issue.table_name} subtasks" +
@@ -40,8 +40,8 @@
         " WHERE subtasks.root_id = #{Issue.table_name}.root_id AND subtasks.lft >= #{Issue.table_name}.lft AND subtasks.rgt <= #{Issue.table_name}.rgt), 0)",
       :default_order => 'desc'),
     QueryColumn.new(:done_ratio, :sortable => "#{Issue.table_name}.done_ratio", :groupable => true),
-    QueryColumn.new(:created_on, :sortable => "#{Issue.table_name}.created_on", :default_order => 'desc'),
-    QueryColumn.new(:closed_on, :sortable => "#{Issue.table_name}.closed_on", :default_order => 'desc'),
+    QueryColumn.new(:created_on, :sortable => "#{Issue.table_name}.created_on", :default_order => 'desc', :groupable => true),
+    QueryColumn.new(:closed_on, :sortable => "#{Issue.table_name}.closed_on", :default_order => 'desc', :groupable => true),
     QueryColumn.new(:relations, :caption => :label_related_issues),
     QueryColumn.new(:description, :inline => false)
   ]