MDEV-7260: Crash in get_best_combination when executing multi-table UPDATE with nested views

Do not use merge_for_insert for commands which use SELECT because optimizer can't work with such tables.

Fixes which makes multi-delete working with normally merged views.

4 files changed, 27 insertions, 2 deletions

diff --git a/sql/sql_base.cc b/sql/sql_base.cc
index 90a12eb366d..3c36c2b514a 100644
--- a/sql/sql_base.cc
+++ b/sql/sql_base.cc
@@ -2028,6 +2028,9 @@ unique_table(THD *thd, TABLE_LIST *table, TABLE_LIST *table_list,
              bool check_alias)
 {
   TABLE_LIST *dup;
+
+  table= table->find_table_for_update();
+
   if (table->table && table->table->file->ht->db_type == DB_TYPE_MRG_MYISAM)
   {
     TABLE_LIST *child;
diff --git a/sql/sql_delete.cc b/sql/sql_delete.cc
index 97d3d10c21c..055b4858598 100644
--- a/sql/sql_delete.cc
+++ b/sql/sql_delete.cc
@@ -657,9 +657,10 @@ multi_delete::initialize_tables(JOIN *join)
   delete_while_scanning= 1;
   for (walk= delete_tables; walk; walk= walk->next_local)
   {
-    tables_to_delete_from|= walk->table->map;
+    TABLE_LIST *tbl= walk->correspondent_table->find_table_for_update();
+    tables_to_delete_from|= tbl->table->map;
     if (delete_while_scanning &&
-        unique_table(thd, walk, join->tables_list, false))
+        unique_table(thd, tbl, join->tables_list, false))
     {
       /*
         If the table we are going to delete from appears
diff --git a/sql/sql_derived.cc b/sql/sql_derived.cc
index 004cccb41a9..56748fa110d 100644
--- a/sql/sql_derived.cc
+++ b/sql/sql_derived.cc
@@ -507,6 +507,9 @@ bool mysql_derived_merge_for_insert(THD *thd, LEX *lex, TABLE_LIST *derived)
     DBUG_RETURN(FALSE);
   if (derived->is_materialized_derived())
     DBUG_RETURN(mysql_derived_prepare(thd, lex, derived));
+  if ((thd->lex->sql_command == SQLCOM_UPDATE_MULTI ||
+       thd->lex->sql_command == SQLCOM_DELETE_MULTI))
+    DBUG_RETURN(FALSE);
   if (!derived->is_multitable())
   {
     if (!derived->single_table_updatable())
diff --git a/sql/table.h b/sql/table.h
index 8e8c2811b71..7a1e380f14c 100644
--- a/sql/table.h
+++ b/sql/table.h
@@ -1984,6 +1984,24 @@ struct TABLE_LIST
   TABLE_LIST *find_underlying_table(TABLE *table);
   TABLE_LIST *first_leaf_for_name_resolution();
   TABLE_LIST *last_leaf_for_name_resolution();
+  /**
+     @brief
+       Find the bottom in the chain of embedded table VIEWs.
+
+     @detail
+       This is used for single-table UPDATE/DELETE when they are modifying a
+       single-table VIEW.
+  */
+  TABLE_LIST *find_table_for_update()
+  {
+    TABLE_LIST *tbl= this;
+    while(!tbl->is_multitable() && tbl->single_table_updatable() &&
+        tbl->merge_underlying_list)
+    {
+      tbl= tbl->merge_underlying_list;
+    }
+    return tbl;
+  }
   TABLE *get_real_join_table();
   bool is_leaf_for_name_resolution();
   inline TABLE_LIST *top_table()