Bug#34773: query with explain extended and derived table / other table

crashes server

When creating temporary table that contains aggregate functions a 
non-reversible source transformation was performed to redirect aggregate
function arguments towards temporary table columns.
This caused EXPLAIN EXTENDED to fail because it was trying to resolve
references to the (freed) temporary table.
Fixed by preserving the original aggregate function arguments and
using them (instead of the transformed ones) for EXPLAIN EXTENDED.

mysql-test/r/explain.result

@@ -107,3 +107,51 @@ X	X	X	X	X	X	X	X	X
 X	X	X	X	X	X	X	X	X	Range checked for each record (index map: 0xFFFFFFFFFF)
 DROP TABLE t2;
 DROP TABLE t1;
+CREATE TABLE t1(a INT);
+CREATE TABLE t2(a INT);
+INSERT INTO t1 VALUES (1),(2);
+INSERT INTO t2 VALUES (1),(2);
+EXPLAIN EXTENDED SELECT 1
+FROM (SELECT COUNT(DISTINCT t1.a) FROM t1,t2 GROUP BY t1.a) AS s1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	PRIMARY	<derived2>	ALL	NULL	NULL	NULL	NULL	2	100.00	
+2	DERIVED	t1	ALL	NULL	NULL	NULL	NULL	2	100.00	Using temporary; Using filesort
+2	DERIVED	t2	ALL	NULL	NULL	NULL	NULL	2	100.00	Using join buffer
+Warnings:
+Note	1003	select 1 AS `1` from (select count(distinct `test`.`t1`.`a`) AS `COUNT(DISTINCT t1.a)` from `test`.`t1` join `test`.`t2` group by `test`.`t1`.`a`) `s1`
+EXPLAIN EXTENDED SELECT 1
+FROM (SELECT COUNT(DISTINCT t1.a) FROM t1,t2 GROUP BY t1.a) AS s1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	PRIMARY	<derived2>	ALL	NULL	NULL	NULL	NULL	2	100.00	
+2	DERIVED	t1	ALL	NULL	NULL	NULL	NULL	2	100.00	Using temporary; Using filesort
+2	DERIVED	t2	ALL	NULL	NULL	NULL	NULL	2	100.00	Using join buffer
+Warnings:
+Note	1003	select 1 AS `1` from (select count(distinct `test`.`t1`.`a`) AS `COUNT(DISTINCT t1.a)` from `test`.`t1` join `test`.`t2` group by `test`.`t1`.`a`) `s1`
+prepare s1 from 
+'EXPLAIN EXTENDED SELECT 1  
+ FROM (SELECT COUNT(DISTINCT t1.a) FROM t1,t2 GROUP BY t1.a) AS s1';
+execute s1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	PRIMARY	<derived2>	ALL	NULL	NULL	NULL	NULL	2	100.00	
+2	DERIVED	t1	ALL	NULL	NULL	NULL	NULL	2	100.00	Using temporary; Using filesort
+2	DERIVED	t2	ALL	NULL	NULL	NULL	NULL	2	100.00	Using join buffer
+Warnings:
+Note	1003	select 1 AS `1` from (select count(distinct `test`.`t1`.`a`) AS `COUNT(DISTINCT t1.a)` from `test`.`t1` join `test`.`t2` group by `test`.`t1`.`a`) `s1`
+prepare s1 from 
+'EXPLAIN EXTENDED SELECT 1  
+ FROM (SELECT COUNT(DISTINCT t1.a) FROM t1,t2 GROUP BY t1.a) AS s1';
+execute s1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	PRIMARY	<derived2>	ALL	NULL	NULL	NULL	NULL	2	100.00	
+2	DERIVED	t1	ALL	NULL	NULL	NULL	NULL	2	100.00	Using temporary; Using filesort
+2	DERIVED	t2	ALL	NULL	NULL	NULL	NULL	2	100.00	Using join buffer
+Warnings:
+Note	1003	select 1 AS `1` from (select count(distinct `test`.`t1`.`a`) AS `COUNT(DISTINCT t1.a)` from `test`.`t1` join `test`.`t2` group by `test`.`t1`.`a`) `s1`
+execute s1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	PRIMARY	<derived2>	ALL	NULL	NULL	NULL	NULL	2	100.00	
+2	DERIVED	t1	ALL	NULL	NULL	NULL	NULL	2	100.00	Using temporary; Using filesort
+2	DERIVED	t2	ALL	NULL	NULL	NULL	NULL	2	100.00	Using join buffer
+Warnings:
+Note	1003	select 1 AS `1` from (select count(distinct `test`.`t1`.`a`) AS `COUNT(DISTINCT t1.a)` from `test`.`t1` join `test`.`t2` group by `test`.`t1`.`a`) `s1`
+DROP TABLE t1,t2;

mysql-test/t/explain.test

@@ -94,4 +94,33 @@ EXPLAIN SELECT 1 FROM
 DROP TABLE t2;
 DROP TABLE t1;
 
+#
+# Bug #34773: query with explain extended and derived table / other table
+# crashes server
+#
+
+CREATE TABLE t1(a INT);
+CREATE TABLE t2(a INT);
+INSERT INTO t1 VALUES (1),(2);
+INSERT INTO t2 VALUES (1),(2);
+
+EXPLAIN EXTENDED SELECT 1
+ FROM (SELECT COUNT(DISTINCT t1.a) FROM t1,t2 GROUP BY t1.a) AS s1;
+
+EXPLAIN EXTENDED SELECT 1
+ FROM (SELECT COUNT(DISTINCT t1.a) FROM t1,t2 GROUP BY t1.a) AS s1;
+
+prepare s1 from 
+'EXPLAIN EXTENDED SELECT 1  
+ FROM (SELECT COUNT(DISTINCT t1.a) FROM t1,t2 GROUP BY t1.a) AS s1';
+execute s1;
+
+prepare s1 from 
+'EXPLAIN EXTENDED SELECT 1  
+ FROM (SELECT COUNT(DISTINCT t1.a) FROM t1,t2 GROUP BY t1.a) AS s1';
+execute s1;
+execute s1;
+
+DROP TABLE t1,t2;
+
 # End of 5.0 tests.

sql/item.cc

@@ -6919,7 +6919,7 @@ enum_field_types Item_type_holder::get_real_type(Item *item)
     */
     Item_sum *item_sum= (Item_sum *) item;
     if (item_sum->keep_field_type())
-      return get_real_type(item_sum->args[0]);
+      return get_real_type(item_sum->get_arg(0));
     break;
   }
   case FUNC_ITEM:
@@ -7182,7 +7182,7 @@ void Item_type_holder::get_full_info(Item *item)
     if (item->type() == Item::SUM_FUNC_ITEM &&
         (((Item_sum*)item)->sum_func() == Item_sum::MAX_FUNC ||
          ((Item_sum*)item)->sum_func() == Item_sum::MIN_FUNC))
-      item = ((Item_sum*)item)->args[0];
+      item = ((Item_sum*)item)->get_arg(0);
     /*
       We can have enum/set type after merging only if we have one enum|set
       field (or MIN|MAX(enum|set field)) and number of NULL fields

sql/item_sum.cc

@@ -369,6 +369,10 @@ Item_sum::Item_sum(List<Item> &list) :arg_count(list.elements),
       args[i++]= item;
     }
   }
+  if (!(orig_args= (Item **) sql_alloc(sizeof(Item *) * arg_count)))
+  {
+    args= NULL;
+  }
   mark_as_sum_func();
   list.empty();					// Fields are used
 }
@@ -379,18 +383,28 @@ Item_sum::Item_sum(List<Item> &list) :arg_count(list.elements),
 */
 
 Item_sum::Item_sum(THD *thd, Item_sum *item):
-  Item_result_field(thd, item), arg_count(item->arg_count),
+  Item_result_field(thd, item),
   aggr_sel(item->aggr_sel),
   nest_level(item->nest_level), aggr_level(item->aggr_level),
-  quick_group(item->quick_group), used_tables_cache(item->used_tables_cache),
+  quick_group(item->quick_group),
+  arg_count(item->arg_count), orig_args(NULL),
+  used_tables_cache(item->used_tables_cache),
   forced_const(item->forced_const) 
 {
   if (arg_count <= 2)
+  {
     args=tmp_args;
+    orig_args=tmp_orig_args;
+  }
   else
+  {
     if (!(args= (Item**) thd->alloc(sizeof(Item*)*arg_count)))
       return;
+    if (!(orig_args= (Item**) thd->alloc(sizeof(Item*)*arg_count)))
+      return;
+  }
   memcpy(args, item->args, sizeof(Item*)*arg_count);
+  memcpy(orig_args, item->orig_args, sizeof(Item*)*arg_count);
 }
 
 
@@ -425,12 +439,13 @@ void Item_sum::make_field(Send_field *tmp_field)
 
 void Item_sum::print(String *str, enum_query_type query_type)
 {
+  Item **pargs= orig_args;
   str->append(func_name());
   for (uint i=0 ; i < arg_count ; i++)
   {
     if (i)
       str->append(',');
-    args[i]->print(str, query_type);
+    pargs[i]->print(str, query_type);
   }
   str->append(')');
 }
@@ -535,6 +550,13 @@ void Item_sum::update_used_tables ()
 }
 
 
+Item *Item_sum::set_arg(int i, THD *thd, Item *new_val) 
+{
+  thd->change_item_tree(args + i, new_val);
+  return new_val;
+}
+
+
 String *
 Item_sum_num::val_str(String *str)
 {
@@ -586,6 +608,7 @@ Item_sum_num::fix_fields(THD *thd, Item **ref)
   if (check_sum_func(thd, ref))
     return TRUE;
 
+  memcpy (orig_args, args, sizeof (Item *) * arg_count);
   fixed= 1;
   return FALSE;
 }
@@ -673,6 +696,7 @@ Item_sum_hybrid::fix_fields(THD *thd, Item **ref)
   if (check_sum_func(thd, ref))
     return TRUE;
 
+  orig_args[0]= args[0];
   fixed= 1;
   return FALSE;
 }
@@ -3141,6 +3165,12 @@ Item_func_group_concat(Name_resolution_context *context_arg,
                                  sizeof(ORDER*)*arg_count_order)))
     return;
 
+  if (!(orig_args= (Item **) sql_alloc(sizeof(Item *) * arg_count)))
+  {
+    args= NULL;
+    return;
+  }
+
   order= (ORDER**)(args + arg_count);
 
   /* fill args items of show and sort */
@@ -3368,6 +3398,7 @@ Item_func_group_concat::fix_fields(THD *thd, Item **ref)
   if (check_sum_func(thd, ref))
     return TRUE;
 
+  memcpy (orig_args, args, sizeof (Item *) * arg_count);
   fixed= 1;
   return FALSE;
 }

sql/item_sum.h

@@ -228,10 +228,8 @@ public:
     VARIANCE_FUNC, SUM_BIT_FUNC, UDF_SUM_FUNC, GROUP_CONCAT_FUNC
   };
 
-  Item **args, *tmp_args[2];
   Item **ref_by; /* pointer to a ref to the object used to register it */
   Item_sum *next; /* next in the circular chain of registered objects  */
-  uint arg_count;
   Item_sum *in_sum_func;  /* embedding set function if any */ 
   st_select_lex * aggr_sel; /* select where the function is aggregated       */ 
   int8 nest_level;        /* number of the nesting level of the set function */
@@ -248,24 +246,32 @@ public:
   List<Item_field> outer_fields;
 
 protected:  
+  uint arg_count;
+  Item **args, *tmp_args[2];
+  /* 
+    Copy of the arguments list to hold the original set of arguments.
+    Used in EXPLAIN EXTENDED instead of the current argument list because 
+    the current argument list can be altered by usage of temporary tables.
+  */
+  Item **orig_args, *tmp_orig_args[2];
   table_map used_tables_cache;
   bool forced_const;
 
 public:  
 
   void mark_as_sum_func();
-  Item_sum() :arg_count(0), quick_group(1), forced_const(FALSE)
+  Item_sum() :quick_group(1), arg_count(0), forced_const(FALSE)
   {
     mark_as_sum_func();
   }
-  Item_sum(Item *a) :args(tmp_args), arg_count(1), quick_group(1), 
-    forced_const(FALSE)
+  Item_sum(Item *a) :quick_group(1), arg_count(1), args(tmp_args),
+    orig_args(tmp_orig_args), forced_const(FALSE)
   {
     args[0]=a;
     mark_as_sum_func();
   }
-  Item_sum( Item *a, Item *b ) :args(tmp_args), arg_count(2), quick_group(1),
-    forced_const(FALSE)
+  Item_sum( Item *a, Item *b ) :quick_group(1), arg_count(2), args(tmp_args),
+    orig_args(tmp_orig_args), forced_const(FALSE)
   {
     args[0]=a; args[1]=b;
     mark_as_sum_func();
@@ -374,6 +380,10 @@ public:
   bool register_sum_func(THD *thd, Item **ref);
   st_select_lex *depended_from() 
     { return (nest_level == aggr_level ? 0 : aggr_sel); }
+
+  Item *get_arg(int i) { return args[i]; }
+  Item *set_arg(int i, THD *thd, Item *new_val);
+  uint get_arg_count() { return arg_count; }
 };
 
 
@@ -981,6 +991,7 @@ public:
     if (udf.fix_fields(thd, this, this->arg_count, this->args))
       return TRUE;
 
+    memcpy (orig_args, args, sizeof (Item *) * arg_count);
     return check_sum_func(thd, ref);
   }
   enum Sumfunctype sum_func () const { return UDF_SUM_FUNC; }

sql/opt_range.cc

@@ -9157,7 +9157,7 @@ get_best_group_min_max(PARAM *param, SEL_TREE *tree)
         DBUG_RETURN(NULL);
 
       /* The argument of MIN/MAX. */
-      Item *expr= min_max_item->args[0]->real_item();    
+      Item *expr= min_max_item->get_arg(0)->real_item();
       if (expr->type() == Item::FIELD_ITEM) /* Is it an attribute? */
       {
         if (! min_max_arg_item)

sql/opt_sum.cc

@@ -199,7 +199,7 @@ int opt_sum_query(TABLE_LIST *tables, List<Item> &all_fields,COND *conds)
           to the number of rows in the tables if this number is exact and
           there are no outer joins.
         */
-        if (!conds && !((Item_sum_count*) item)->args[0]->maybe_null &&
+        if (!conds && !((Item_sum_count*) item)->get_arg(0)->maybe_null &&
             !outer_tables && maybe_exact_count)
         {
           if (!is_exact_count)
@@ -225,7 +225,7 @@ int opt_sum_query(TABLE_LIST *tables, List<Item> &all_fields,COND *conds)
           parts of the key is found in the COND, then we can use
           indexes to find the key.
         */
-        Item *expr=item_sum->args[0];
+        Item *expr=item_sum->get_arg(0);
         if (expr->real_item()->type() == Item::FIELD_ITEM)
         {
           uchar key_buff[MAX_KEY_LENGTH];
@@ -373,7 +373,7 @@ int opt_sum_query(TABLE_LIST *tables, List<Item> &all_fields,COND *conds)
           parts of the key is found in the COND, then we can use
           indexes to find the key.
         */
-        Item *expr=item_sum->args[0];
+        Item *expr=item_sum->get_arg(0);
         if (expr->real_item()->type() == Item::FIELD_ITEM)
         {
           uchar key_buff[MAX_KEY_LENGTH];

sql/sql_select.cc

@@ -9780,11 +9780,11 @@ create_tmp_table(THD *thd,TMP_TABLE_PARAM *param,List<Item> &fields,
     }
     if (type == Item::SUM_FUNC_ITEM && !group && !save_sum_fields)
     {						/* Can't calc group yet */
-      ((Item_sum*) item)->result_field=0;
-      for (i=0 ; i < ((Item_sum*) item)->arg_count ; i++)
+      Item_sum *sum_item= (Item_sum *) item;
+      sum_item->result_field=0;
+      for (i=0 ; i < sum_item->get_arg_count() ; i++)
       {
-	Item **argp= ((Item_sum*) item)->args + i;
-	Item *arg= *argp;
+	Item *arg= sum_item->get_arg(i);
 	if (!arg->const_item())
 	{
 	  Field *new_field=
@@ -9812,7 +9812,7 @@ create_tmp_table(THD *thd,TMP_TABLE_PARAM *param,List<Item> &fields,
             string_total_length+= new_field->pack_length();
           }
           thd->mem_root= mem_root_save;
-          thd->change_item_tree(argp, new Item_field(new_field));
+          arg= sum_item->set_arg(i, thd, new Item_field(new_field));
           thd->mem_root= &table->mem_root;
 	  if (!(new_field->flags & NOT_NULL_FLAG))
           {
@@ -9821,7 +9821,7 @@ create_tmp_table(THD *thd,TMP_TABLE_PARAM *param,List<Item> &fields,
               new_field->maybe_null() is still false, it will be
               changed below. But we have to setup Item_field correctly
             */
-            (*argp)->maybe_null=1;
+            arg->maybe_null=1;
           }
           new_field->field_index= fieldnr++;
 	}
@@ -14491,9 +14491,9 @@ count_field_types(SELECT_LEX *select_lex, TMP_TABLE_PARAM *param,
             param->quick_group=0;			// UDF SUM function
           param->sum_func_count++;
 
-          for (uint i=0 ; i < sum_item->arg_count ; i++)
+          for (uint i=0 ; i < sum_item->get_arg_count() ; i++)
           {
-            if (sum_item->args[0]->real_item()->type() == Item::FIELD_ITEM)
+            if (sum_item->get_arg(i)->real_item()->type() == Item::FIELD_ITEM)
               param->field_count++;
             else
               param->func_count++;