MDEV-17017 Explain for query using derived table specified with

           a table value constructor shows wrong number of rows

This is another attempt to fix this bug. The previous patch did not take
into account that a transformation for ALL/ANY subqueries could be applied
to the materialized table that wrapped the table value constructor used as
a specification of the subselect used an ALL/ANY subquery. In this case
the result of the derived table used a sink of the class select_subselect
rather than of the class select_unit. Thus the previous fix could cause
memory overwrites when running EXPLAIN for queries with table value
constructors in ALL/ANY subselects.

mysql-test/main/table_value_constr.test

@@ -1123,5 +1123,3 @@ PREPARE stmt FROM "SELECT * FROM (VALUES(1 + 1,2,'abc')) t";
 EXECUTE stmt;
 EXECUTE stmt;
 DEALLOCATE PREPARE stmt;
-
-

sql/sql_class.h

@@ -4956,7 +4956,8 @@ class select_result :public select_result_sink
   SELECT_LEX_UNIT *unit;
   /* Something used only by the parser: */
 public:
-  select_result(THD *thd_arg): select_result_sink(thd_arg) {}
+  ha_rows est_records;  /* estimated number of records in the result */
+ select_result(THD *thd_arg): select_result_sink(thd_arg), est_records(0) {}
   void set_unit(SELECT_LEX_UNIT *unit_arg) { unit= unit_arg; }
   virtual ~select_result() {};
   /**
@@ -5528,7 +5529,6 @@ class select_unit :public select_result_interceptor
   TMP_TABLE_PARAM tmp_table_param;
   int write_err; /* Error code from the last send_data->ha_write_row call. */
   TABLE *table;
-  ha_rows records;
 
   select_unit(THD *thd_arg):
     select_result_interceptor(thd_arg),
@@ -5566,7 +5566,6 @@ class select_unit :public select_result_interceptor
     curr_sel= UINT_MAX;
     step= UNION_TYPE;
     write_err= 0;
-    records= 0;
   }
   void change_select();
 };

sql/sql_lex.cc

@@ -4678,18 +4678,18 @@ void SELECT_LEX::increase_derived_records(ha_rows records)
       return; 
   }
 
-  select_unit *result= (select_unit*)unit->result;
+  select_result *result= unit->result;
   switch (linkage)
   {
   case INTERSECT_TYPE:
     // result of intersect can't be more then one of components
-    set_if_smaller(result->records, records);
+    set_if_smaller(result->est_records, records);
   case EXCEPT_TYPE:
     // in worse case none of record will be removed
     break;
   default:
     // usual UNION
-    result->records+= records;
+    result->est_records+= records;
     break;
   }
 }

sql/table.cc

@@ -8334,7 +8334,7 @@ int TABLE_LIST::fetch_number_of_rows()
   }
   if (is_materialized_derived() && !fill_me)
   {
-    table->file->stats.records= ((select_unit*)(get_unit()->result))->records;
+    table->file->stats.records= get_unit()->result->est_records;
     set_if_bigger(table->file->stats.records, 2);
     table->used_stat_records= table->file->stats.records;
   }