Make window functions computation step show up in EXPLAIN FORMAT=JSON output

mysql-test/r/win.result

@@ -1401,3 +1401,76 @@ pk	c	CNT
 9	2	4
 10	2	3
 drop table t0,t1;
+#
+# EXPLAIN FORMAT=JSON support for window functions
+#
+create table t0 (a int);
+insert into t0 values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
+explain format=json select rank() over (order by a) from t0;
+EXPLAIN
+{
+  "query_block": {
+    "select_id": 1,
+    "window_functions_computation": {
+      "temporary_table": {
+        "table": {
+          "table_name": "t0",
+          "access_type": "ALL",
+          "rows": 10,
+          "filtered": 100
+        }
+      }
+    }
+  }
+}
+create table t1 (a int, b int, c int);
+insert into t1 select a,a,a from t0;
+explain format=json
+select
+a,
+rank() over (order by sum(b))
+from t1
+group by a;
+EXPLAIN
+{
+  "query_block": {
+    "select_id": 1,
+    "filesort": {
+      "window_functions_computation": {
+        "temporary_table": {
+          "table": {
+            "table_name": "t1",
+            "access_type": "ALL",
+            "rows": 10,
+            "filtered": 100
+          }
+        }
+      }
+    }
+  }
+}
+explain format=json
+select
+a,
+rank() over (order by sum(b))
+from t1
+group by a
+order by null;
+EXPLAIN
+{
+  "query_block": {
+    "select_id": 1,
+    "window_functions_computation": {
+      "temporary_table": {
+        "table": {
+          "table_name": "t1",
+          "access_type": "ALL",
+          "rows": 10,
+          "filtered": 100
+        }
+      }
+    }
+  }
+}
+drop table t1;
+drop table t0;

mysql-test/t/win.test

@@ -924,8 +924,33 @@ execute stmt;
 
 drop table t0,t1;
 
+--echo #
+--echo # EXPLAIN FORMAT=JSON support for window functions
+--echo #
+create table t0 (a int);
+insert into t0 values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
 
+explain format=json select rank() over (order by a) from t0;
 
+create table t1 (a int, b int, c int);
+insert into t1 select a,a,a from t0;
 
+explain format=json
+select
+  a,
+  rank() over (order by sum(b))
+from t1
+group by a;
+
+explain format=json
+select
+  a,
+  rank() over (order by sum(b))
+from t1
+group by a
+order by null;
+
+drop table t1;
+drop table t0;
 
 

sql/sql_explain.cc

@@ -878,6 +878,9 @@ void Explain_select::print_explain_json(Explain_query *query,
         case AGGR_OP_REMOVE_DUPLICATES:
           writer->add_member("duplicate_removal").start_object();
           break;
+        case AGGR_OP_WINDOW_FUNCS:
+          writer->add_member("window_functions_computation").start_object();
+          break;
         default:
           DBUG_ASSERT(0);
       }

sql/sql_explain.h

@@ -264,7 +264,8 @@ typedef enum
   AGGR_OP_TEMP_TABLE,
   AGGR_OP_FILESORT,
   //AGGR_OP_READ_SORTED_FILE, // need this?
-  AGGR_OP_REMOVE_DUPLICATES
+  AGGR_OP_REMOVE_DUPLICATES,
+  AGGR_OP_WINDOW_FUNCS
   //AGGR_OP_JOIN // Need this?
 } enum_explain_aggr_node_type;
 
@@ -296,6 +297,11 @@ class Explain_aggr_remove_dups : public Explain_aggr_node
   enum_explain_aggr_node_type get_type() { return AGGR_OP_REMOVE_DUPLICATES; }
 };
 
+class Explain_aggr_window_funcs : public Explain_aggr_node
+{
+public:
+  enum_explain_aggr_node_type get_type() { return AGGR_OP_WINDOW_FUNCS; }
+};
 
 /////////////////////////////////////////////////////////////////////////////
 

sql/sql_select.cc

@@ -2135,7 +2135,6 @@ bool JOIN::make_aggr_tables_info()
     All optimization is done. Check if we can use the storage engines
     group by handler to evaluate the group by
   */
-  group_by_handler *gbh= NULL;
   if (tables_list && (tmp_table_param.sum_func_count || group_list) &&
       !procedure)
   {
@@ -2337,8 +2336,8 @@ bool JOIN::make_aggr_tables_info()
     // psergey-todo: this is probably an incorrect place:
     if (select_lex->window_funcs.elements)
     {
-      curr_tab->window_funcs= new Window_funcs_computation;
-      if (curr_tab->window_funcs->setup(thd, &select_lex->window_funcs))
+      curr_tab->window_funcs_step= new Window_funcs_computation;
+      if (curr_tab->window_funcs_step->setup(thd, &select_lex->window_funcs))
         DBUG_RETURN(true);
     }
 
@@ -19137,7 +19136,10 @@ bool test_if_use_dynamic_range_scan(JOIN_TAB *join_tab)
 int join_init_read_record(JOIN_TAB *tab)
 {
   int error;
-
+  /* 
+    Note: the query plan tree for the below operations is constructed in
+    save_agg_explain_data.
+  */
   if (tab->distinct && tab->remove_duplicates())  // Remove duplicates.
     return 1;
   if (tab->filesort && tab->sort_table())     // Sort table.
@@ -24158,6 +24160,14 @@ void save_agg_explain_data(JOIN *join, Explain_select *xpl_sel)
     node= new Explain_aggr_tmp_table;
     node->child= prev_node;
 
+    if (join_tab->window_funcs_step)
+    {
+      prev_node=node;
+      node= new Explain_aggr_window_funcs;
+      node->child= prev_node;
+    }
+
+    /* The below matches execution in join_init_read_record() */
     if (join_tab->distinct)
     {
       prev_node= node;
@@ -25919,9 +25929,10 @@ AGGR_OP::end_send()
 
   // Update ref array
   join_tab->join->set_items_ref_array(*join_tab->ref_array);
-  if (join_tab->window_funcs)
+  if (join_tab->window_funcs_step)
   {
-    join_tab->window_funcs->exec(join);
+    if (join_tab->window_funcs_step->exec(join))
+      return NESTED_LOOP_ERROR;
   }
 
   table->reginfo.lock_type= TL_UNLOCK;

sql/sql_select.h

@@ -428,7 +428,7 @@ typedef struct st_join_table {
     Non-NULL value means this join_tab must do window function computation
     before reading.
   */
-  Window_funcs_computation* window_funcs;
+  Window_funcs_computation* window_funcs_step;
 
   /**
     List of topmost expressions in the select list. The *next* JOIN TAB