EXPLAIN UPDATE/DELETE

- Make EXPLAIN UPDATE/DELETE work inside SPs
- Return correct error code from mysql_delete()
- EXPLAIN <multi-DELETE> will create a multi_delete object (as it 
  affects the optimization). select_result will be only used for 
  producing EXPLAIN output.

mysql-test/r/explain_non_select.result

@@ -49,7 +49,7 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 explain delete t1 from t0, t1 where t0.a = t1.a;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t0	ALL	NULL	NULL	NULL	NULL	8	Using where
-1	SIMPLE	t1	ref	a	a	5	test.t0.a	4	Using index
+1	SIMPLE	t1	ref	a	a	5	test.t0.a	4	
 drop table t0, t1;
 # ###################################################################
 # ## EXPLAIN UPDATE tests

sql/sp_head.cc

@@ -313,14 +313,26 @@ sp_get_flags_for_command(LEX *lex)
     flags= sp_head::HAS_COMMIT_OR_ROLLBACK;
     break;
   case SQLCOM_DELETE:
+  case SQLCOM_DELETE_MULTI:
   {
-    if (lex->select_lex.item_list.is_empty())
+    /* 
+      DELETE normally doesn't return resultset, but there are two exceptions:
+       - DELETE ... RETURNING
+       - EXPLAIN DELETE ...
+    */
+    if (lex->select_lex.item_list.is_empty() && !lex->describe)
       flags= 0;
     else
-    {
-      /* This is DELETE ... RETURNING ...  */
       flags= sp_head::MULTI_RESULTS; 
+    break;
   }
+  case SQLCOM_UPDATE:
+  case SQLCOM_UPDATE_MULTI:
+  {
+    if (!lex->describe)
+      flags= 0;
+    else
+      flags= sp_head::MULTI_RESULTS; 
     break;
   }
   default:
@@ -2988,7 +3000,6 @@ sp_lex_keeper::reset_lex_and_exec_core(THD *thd, uint *nextp,
   }
 
   reinit_stmt_before_use(thd, m_lex);
-  // not here, but inside every instr: create_qpf_query(m_lex);
 
   if (open_tables)
     res= instr->exec_open_and_lock_tables(thd, m_lex->query_tables);

sql/sql_delete.cc

@@ -183,7 +183,6 @@ bool mysql_delete(THD *thd, TABLE_LIST *table_list, COND *conds,
   bool          const_cond_result;
   ha_rows	deleted= 0;
   bool          reverse= FALSE;
-  bool          err= true;
   ORDER *order= (ORDER *) ((order_list && order_list->elements) ?
                            order_list->first : NULL);
   SELECT_LEX   *select_lex= &thd->lex->select_lex;
@@ -659,7 +658,7 @@ exit_without_my_ok:
   List<Item> dummy; /* note: looked in 5.6 and they too use a dummy list like this */
   result2->prepare(dummy, &thd->lex->unit);
   thd->send_explain_fields(result2);
-  int err2= thd->lex->query_plan_footprint->print_explain(result2, 0 /* explain flags*/);
+  int err2= thd->lex->query_plan_footprint->print_explain(result2, thd->lex->describe);
 
   if (err2)
     result2->abort_result_set();
@@ -669,7 +668,7 @@ exit_without_my_ok:
   delete select;
   free_underlaid_joins(thd, select_lex);
   //table->set_keyread(false);
-  DBUG_RETURN((err || thd->is_error() || thd->killed) ? 1 : 0);
+  DBUG_RETURN((err2 || thd->is_error() || thd->killed) ? 1 : 0);
 }
 
 

sql/sql_parse.cc

@@ -3332,18 +3332,7 @@ end_with_restore_list:
 
     if (!thd->is_fatal_error)
     {
-      if (explain)
-      {
-        result= new select_send();
-        if (thd->send_explain_fields(result))
-        {
-          delete result;
-          result= NULL;
-        }
-      }
-      else
       result= new multi_delete(aux_tables, lex->table_count);
-
       if (result)
       {
         res= mysql_select(thd, &select_lex->ref_pointer_array,
@@ -3362,20 +3351,22 @@ end_with_restore_list:
         if (!explain)
         {
           MYSQL_MULTI_DELETE_DONE(res, del_result->num_deleted());
-        }
-        else
-        {
-          result->reset_offset_limit(); 
-          thd->lex->query_plan_footprint->print_explain(result, 
-                                                        thd->lex->describe);
-        }
-      
           if (res)
             result->abort_result_set(); /* for both DELETE and EXPLAIN DELETE */
+        }
         else
         {
-          if (explain)
+          if (!res)
-            result->send_eof(); 
+          {
+            select_result *result= new select_send();
+            LEX *lex= thd->lex;
+            if (thd->send_explain_fields(result) ||
+                lex->query_plan_footprint->print_explain(result, lex->describe) ||
+                result->send_eof())
+              res= 1;
+          }
+          else
+            result->abort_result_set(); /* for both DELETE and EXPLAIN DELETE */
         }
         delete result;
       }

sql/sql_select.cc

@@ -22990,10 +22990,13 @@ int JOIN::save_qpf(QPF_query *output, bool need_tmp_table, bool need_order,
        unit= unit->next_unit())
   {
     /* 
-      Display subqueries only if they are not parts of eliminated WHERE/ON
+      Display subqueries only if 
-      clauses.
+      (1) they are not parts of ON clauses that were eliminated by table 
+          elimination.
+      (2) they are not merged derived tables
     */
-    if (!(unit->item && unit->item->eliminated))
+    if (!(unit->item && unit->item->eliminated) &&                    // (1)
+        (!unit->derived || unit->derived->is_materialized_derived())) // (2)
     {
       qp_node->add_child(unit->first_select()->select_number);
     }

sql/sql_update.cc

@@ -1039,8 +1039,8 @@ exit_without_my_ok:
   List<Item> dummy; /* note: looked in 5.6 and they too use a dummy list like this */
   result->prepare(dummy, &thd->lex->unit);
   thd->send_explain_fields(result);
-  int err2= thd->lex->query_plan_footprint->print_explain(result, 0 /* explain flags*/);
+  int err2= thd->lex->query_plan_footprint->print_explain(result,
-
+                                                          thd->lex->describe);
   if (err2)
     result->abort_result_set();
   else
@@ -1048,7 +1048,7 @@ exit_without_my_ok:
 
   delete select;
   free_underlaid_joins(thd, select_lex);
-  DBUG_RETURN((error >= 0 || thd->is_error()) ? 1 : 0);
+  DBUG_RETURN((err2 || thd->is_error()) ? 1 : 0);
 }
 
 /*
@@ -1518,7 +1518,7 @@ bool mysql_multi_update(THD *thd,
   {
     if (explain)
     {
-      thd->lex->query_plan_footprint->print_explain(output, 0);
+      thd->lex->query_plan_footprint->print_explain(output, thd->lex->describe);
       output->send_eof(); 
       delete output;
     }