diff --git a/sql/item_windowfunc.cc b/sql/item_windowfunc.cc
index bf0d06b8837..82e84ab5c36 100644
--- a/sql/item_windowfunc.cc
+++ b/sql/item_windowfunc.cc
@@ -56,6 +56,8 @@ Item_window_func::fix_fields(THD *thd, Item **ref)
   if (window_func->fix_fields(thd, ref))
     return true;
 
+  fix_length_and_dec();
+
   max_length= window_func->max_length;
 
   fixed= 1;
@@ -180,3 +182,27 @@ void Item_window_func::advance_window()
   }
   window_func->add();
 }
+
+bool Item_sum_percent_rank::add()
+{
+  row_number++;
+  if (test_if_group_changed(orderby_fields) > -1)
+  {
+    /* Row value changed. */
+    cur_rank= row_number;
+  }
+  return false;
+}
+
+void Item_sum_percent_rank::setup_window_func(THD *thd, Window_spec *window_spec)
+{
+  /* TODO: move this into Item_window_func? */
+  for (ORDER *curr= window_spec->order_list.first; curr; curr=curr->next)
+  {
+    Cached_item *tmp= new_Cached_item(thd, curr->item[0], TRUE);
+    orderby_fields.push_back(tmp);
+  }
+  clear();
+}
+
+
diff --git a/sql/item_windowfunc.h b/sql/item_windowfunc.h
index 6277183ce58..5cb1e8aae32 100644
--- a/sql/item_windowfunc.h
+++ b/sql/item_windowfunc.h
@@ -70,6 +70,7 @@ public:
 
 class Item_sum_rank: public Item_sum_int
 {
+protected:
   longlong row_number; // just ROW_NUMBER()
   longlong cur_rank;   // current value
   
@@ -108,7 +109,7 @@ public:
   {
     return "rank";
   }
-  
+
   void setup_window_func(THD *thd, Window_spec *window_spec);
 };
 
@@ -168,6 +169,103 @@ class Item_sum_dense_rank: public Item_sum_int
 
 };
 
+/* TODO-cvicentiu
+ * Perhaps this is overengineering, but I would like to decouple the 2-pass
+ * algorithm from the specific action that must be performed during the
+ * first pass. The second pass can make use of the "add" function from the
+ * Item_sum_<window_function>.
+ */
+
+/*
+   This class represents a generic interface for window functions that need
+   to store aditional information. Such window functions include percent_rank
+   and cume_dist.
+*/
+class Window_context
+{
+ public:
+  virtual void add_field_to_context(Field* field) = 0;
+  virtual void reset() = 0;
+  virtual ~Window_context() {};
+};
+
+/*
+   A generic interface that specifies the datatype that the context represents.
+*/
+template <typename T>
+class Window_context_getter
+{
+ protected:
+  virtual T get_field_context(const Field* field) = 0;
+  virtual ~Window_context_getter() {};
+};
+
+/*
+   A window function context representing the number of rows that are present
+   with a partition. Because the number of rows is not dependent of the
+   specific value within the current field, we ignore the parameter
+   in this case.
+*/
+class Window_context_row_count :
+  public Window_context, Window_context_getter<ulonglong>
+{
+ public:
+  Window_context_row_count() : num_rows_(0) {};
+
+  void add_field_to_context(Field* field __attribute__((unused)))
+  {
+    num_rows_++;
+  }
+
+  void reset()
+  {
+    num_rows_= 0;
+  }
+
+  ulonglong get_field_context(const Field* field __attribute__((unused)))
+  {
+    return num_rows_;
+  }
+ private:
+  ulonglong num_rows_;
+};
+
+class Window_context_row_and_group_count :
+  public Window_context, Window_context_getter<std::pair<ulonglong, ulonglong> >
+{
+ public:
+  Window_context_row_and_group_count(void * group_list) {}
+};
+
+/*
+  An abstract class representing an item that holds a context.
+*/
+class Item_context
+{
+ public:
+  Item_context() : context_(NULL) {}
+  Window_context* get_window_context() { return context_; }
+
+  virtual bool create_window_context() = 0;
+  virtual void delete_window_context() = 0;
+
+ protected:
+  Window_context* context_;
+};
+
+/*
+  A base window function (aggregate) that also holds a context.
+
+  NOTE: All two pass window functions need to implement
+  this interface.
+*/
+class Item_sum_window_with_context : public Item_sum_num,
+                                     public Item_context
+{
+ public:
+  Item_sum_window_with_context(THD *thd)
+   : Item_sum_num(thd), Item_context() {}
+};
 
 /*
   @detail
@@ -177,23 +275,43 @@ class Item_sum_dense_rank: public Item_sum_int
 
   Computation of this function requires two passes:
   - First pass to find #rows in the partition
+    This is held within the row_count context.
   - Second pass to compute rank of current row and the value of the function
 */
-
-class Item_sum_percent_rank: public Item_sum_num
+class Item_sum_percent_rank: public Item_sum_window_with_context,
+                             public Window_context_row_count
 {
-  longlong rank;
-  longlong partition_rows;
-
-  void clear() {}
-  bool add() { return false; }
-  void update_field() {}
-
  public:
   Item_sum_percent_rank(THD *thd)
-    : Item_sum_num(thd), rank(0), partition_rows(0) {}
+    : Item_sum_window_with_context(thd), cur_rank(1) {}
 
-  double val_real() { return 0; }
+  longlong val_int()
+  {
+   /*
+      Percent rank is a real value so calling the integer value should never
+      happen. It makes no sense as it gets truncated to either 0 or 1.
+   */
+    DBUG_ASSERT(0);
+    return 0;
+  }
+
+  double val_real()
+  {
+   /*
+     We can not get the real value without knowing the number of rows
+     in the partition. Don't divide by 0.
+   */
+   if (!get_context_())
+   {
+     // Calling this kind of function with a context makes no sense.
+     DBUG_ASSERT(0);
+     return 0;
+   }
+
+   longlong partition_rows = get_context_()->get_field_context(result_field);
+   return partition_rows > 1 ?
+             static_cast<double>(cur_rank - 1) / (partition_rows - 1) : 0;
+  }
 
   enum Sumfunctype sum_func () const
   {
@@ -204,12 +322,61 @@ class Item_sum_percent_rank: public Item_sum_num
   {
     return "percent_rank";
   }
-  
+
+  bool create_window_context()
+  {
+    // TODO-cvicentiu: Currently this means we must make sure to delete
+    // the window context. We can potentially allocate this on the THD memroot.
+    // At the same time, this is only necessary for a small portion of the
+    // query execution and it does not make sense to keep it for all of it.
+    context_ = new Window_context_row_count();
+    if (context_ == NULL)
+      return true;
+    return false;
+  }
+
+  void delete_window_context()
+  {
+    if (context_)
+      delete get_context_();
+    context_ = NULL;
+  }
+
+  void update_field() {}
+
+  void clear()
+  {
+    cur_rank= 1;
+    row_number= 0;
+  }
+  bool add();
+  enum Item_result result_type () const { return REAL_RESULT; }
   enum_field_types field_type() const { return MYSQL_TYPE_DOUBLE; }
 
+  void fix_length_and_dec()
+  {
+    decimals = 10;  // TODO-cvicentiu find out how many decimals the standard
+                    // requires.
+  }
+
+  void setup_window_func(THD *thd, Window_spec *window_spec);
+
+ private:
+  longlong cur_rank;   // Current rank of the current row.
+  longlong row_number; // Value if this were ROW_NUMBER() function.
+
+  List<Cached_item> orderby_fields;
+
+  /* Helper function so that we don't cast the context every time. */
+  Window_context_row_count* get_context_()
+  {
+    return static_cast<Window_context_row_count *>(context_);
+  }
 };
 
 
+
+
 /*
   @detail
   "The relative rank of a row R is defined as NP/NR, where 
@@ -221,18 +388,11 @@ class Item_sum_percent_rank: public Item_sum_num
   two passes.
 */
 
-class Item_sum_cume_dist: public Item_sum_num
+class Item_sum_cume_dist: public Item_sum_percent_rank
 {
-  longlong count;
-  longlong partition_rows;
-
-  void clear() {}
-  bool add() { return false; }
-  void update_field() {}
-
  public:
   Item_sum_cume_dist(THD *thd)
-    : Item_sum_num(thd), count(0), partition_rows(0) {}
+    : Item_sum_percent_rank(thd) {}
 
   double val_real() { return 0; }
 
@@ -245,9 +405,6 @@ class Item_sum_cume_dist: public Item_sum_num
   {
     return "cume_dist";
   }
-
-  enum_field_types field_type() const { return MYSQL_TYPE_DOUBLE; }
- 
 };
 
 
@@ -331,7 +488,7 @@ public:
   }
 
   longlong val_int()
-  { 
+  {
     if (force_return_blank)
       return 0;
     return read_value_from_result_field? result_field->val_int() : 
@@ -361,15 +518,14 @@ public:
                               List<Item> &fields, uint flags);
   void fix_length_and_dec()
   {
-    window_func->fix_length_and_dec();
+    decimals = window_func->decimals;
   }
 
   const char* func_name() const { return "WF"; }
 
   bool fix_fields(THD *thd, Item **ref);
-  
-  bool resolve_window_name(THD *thd);
 
+  bool resolve_window_name(THD *thd);
 };
 
 #endif /* ITEM_WINDOWFUNC_INCLUDED */
diff --git a/sql/sql_window.cc b/sql/sql_window.cc
index c7dcfb73341..29fa938a2a6 100644
--- a/sql/sql_window.cc
+++ b/sql/sql_window.cc
@@ -705,6 +705,110 @@ bool compute_window_func_with_frames(Item_window_func *item_win,
 }
 
 
+bool compute_two_pass_window_functions(Item_window_func *item_win,
+                                       TABLE *table, READ_RECORD *info)
+{
+  /* Perform first pass. */
+
+  // TODO-cvicentiu why not initialize the record for when we need, _in_
+  // this function.
+  READ_RECORD *info2= new READ_RECORD();
+  int err;
+  bool is_error = false;
+  bool first_row= true;
+  clone_read_record(info, info2);
+  Item_sum_window_with_context *window_func= 
+    static_cast<Item_sum_window_with_context *>(item_win->window_func);
+  uchar *rowid_buf= (uchar*) my_malloc(table->file->ref_length, MYF(0));
+
+  is_error= window_func->create_window_context();
+  /* Unable to allocate a new context. */
+  if (is_error)
+    return true;
+
+  Window_context *context = window_func->get_window_context();
+  /*
+     The two pass algorithm is as follows:
+     We have a sorted table according to the partition and order by clauses.
+     1. Scan through the table till we reach a partition boundary.
+     2. For each row that we scan, add it to the context.
+     3. Once the partition boundary is met, do a second scan through the
+     current partition and use the context information to compute the value for
+     the window function for that partition.
+     4. Reset the context.
+     5. Repeat from 1 till end of table.
+  */
+
+  bool done = false;
+  longlong rows_in_current_partition = 0;
+  // TODO handle end of table updating.
+  while (!done)
+  {
+
+    if ((err= info->read_record(info)))
+    {
+      done = true;
+    }
+
+    bool partition_changed= (done || item_win->check_partition_bound() > -1) ?
+                              true : false;
+    // The first time we always have a partition changed. Ignore it.
+    if (first_row)
+    {
+      partition_changed= false;
+      first_row= false;
+    }
+
+    if (partition_changed)
+    {
+      /*
+         We are now looking at the first row for the next partition, or at the
+         end of the table. Either way, we must remember this position for when
+         we finish doing the second pass.
+      */
+      table->file->position(table->record[0]);
+      memcpy(rowid_buf, table->file->ref, table->file->ref_length);
+
+      for (longlong row_number = 0; row_number < rows_in_current_partition;
+          row_number++)
+      {
+        if ((err= info2->read_record(info2)))
+        {
+          is_error= true;
+          break;
+        }
+        window_func->add();
+        // Save the window function into the table.
+        item_win->save_in_field(item_win->result_field, true);
+        err= table->file->ha_update_row(table->record[1], table->record[0]);
+        if (err && err != HA_ERR_RECORD_IS_THE_SAME)
+        {
+          is_error= true;
+          break;
+        }
+      }
+
+      if (is_error)
+        break;
+
+      rows_in_current_partition= 0;
+      window_func->clear();
+      context->reset();
+
+      // Return to the beginning of the new partition.
+      table->file->ha_rnd_pos(table->record[0], rowid_buf);
+    }
+    rows_in_current_partition++;
+    context->add_field_to_context(item_win->result_field);
+  }
+
+  window_func->delete_window_context();
+  delete info2;
+  my_free(rowid_buf);
+  return is_error;
+}
+
+
 /*
   @brief
     This function is called by JOIN::exec to compute window function values
@@ -899,6 +1003,13 @@ bool JOIN::process_window_functions(List<Item> *curr_fields_list)
                 is_error= true;
               break;
             }
+          case Item_sum::PERCENT_RANK_FUNC:
+          case Item_sum::CUME_DIST_FUNC:
+            {
+              if (compute_two_pass_window_functions(item_win, tbl, &info))
+                is_error= true;
+              break;
+            }
           case Item_sum::COUNT_FUNC:
           {
             /*