Implement DENSE_RANK function.

mysql-test/r/win.result

@@ -92,3 +92,46 @@ pk	a	rank() over (order by a)
 9	4	9
 10	4	9
 drop table t2;
+#
+# Try DENSE_RANK() function
+#
+create table t3 (
+pk int primary key,
+a int,
+b int
+);
+insert into t3 values
+( 1 , 0, 10),
+( 2 , 0, 10),
+( 3 , 1, 10),
+( 4 , 1, 10),
+( 8 , 2, 10),
+( 5 , 2, 20),
+( 6 , 2, 20),
+( 7 , 2, 20),
+( 9 , 4, 20),
+(10 , 4, 20);
+select pk, a, b, rank() over (order by a), dense_rank() over (order by a) from t3;
+pk	a	b	rank() over (order by a)	dense_rank() over (order by a)
+1	0	10	1	1
+2	0	10	1	1
+3	1	10	3	2
+4	1	10	3	2
+8	2	10	5	3
+5	2	20	5	3
+6	2	20	5	3
+7	2	20	5	3
+9	4	20	9	4
+10	4	20	9	4
+select pk, a, b, rank() over (partition by b order by a), dense_rank() over (partition by b order by a) from t3;
+pk	a	b	rank() over (partition by b order by a)	dense_rank() over (partition by b order by a)
+1	0	10	1	1
+2	0	10	1	1
+3	1	10	3	2
+4	1	10	3	2
+8	2	10	5	3
+5	2	20	1	1
+6	2	20	1	1
+7	2	20	1	1
+9	4	20	4	2
+10	4	20	4	2

mysql-test/t/win.test

@@ -85,3 +85,29 @@ select pk, a, rank() over (order by a) from t2;
 
 drop table t2;
 
+--echo #
+--echo # Try DENSE_RANK() function
+--echo #
+create table t3 (
+  pk int primary key,
+  a int,
+  b int
+);
+
+insert into t3 values
+( 1 , 0, 10),
+( 2 , 0, 10),
+( 3 , 1, 10),
+( 4 , 1, 10),
+( 8 , 2, 10),
+( 5 , 2, 20),
+( 6 , 2, 20),
+( 7 , 2, 20),
+( 9 , 4, 20),
+(10 , 4, 20);
+
+select pk, a, b, rank() over (order by a), dense_rank() over (order by a) from t3;
+select pk, a, b, rank() over (partition by b order by a), dense_rank() over (partition by b order by a) from t3;
+
+drop table tr;
+

sql/item_windowfunc.cc

@@ -55,6 +55,24 @@ void Item_sum_rank::setup_window_func(THD *thd, Window_spec *window_spec)
   clear();
 }
 
+void Item_sum_dense_rank::setup_window_func(THD *thd, Window_spec *window_spec)
+{
+  /* TODO: consider moving this && Item_sum_rank's implementation */
+  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();
+}
+
+bool Item_sum_dense_rank::add()
+{
+  if (test_if_group_changed(orderby_fields) > -1)
+   dense_rank++;
+
+  return false;
+}
+
 
 bool Item_sum_rank::add()
 {

sql/item_windowfunc.h

@@ -135,7 +135,7 @@ class Item_sum_rank: public Item_sum_int
 
 
 /*
-  RANK() OVER (...) Windowing function
+  DENSE_RANK() OVER (...) Windowing function
 
   @detail
   - This is a Window function (not just an aggregate)
@@ -156,11 +156,16 @@ class Item_sum_rank: public Item_sum_int
 class Item_sum_dense_rank: public Item_sum_int
 {
   longlong dense_rank;
-  
+  List<Cached_item> orderby_fields;
   /* TODO: implementation is missing */
-  void clear() {}
-  bool add() { return false; }
+  void clear() {
+    dense_rank= 1;
+  }
+  bool add();
   void update_field() {}
+  longlong val_int() {
+    return dense_rank;
+  }
 
  public:
   Item_sum_dense_rank(THD *thd)
@@ -175,6 +180,8 @@ class Item_sum_dense_rank: public Item_sum_int
     return "dense_rank";
   }
 
+  void setup_window_func(THD *thd, Window_spec *window_spec);
+
 };