MDEV-6879: Dereference of NULL primary_file->table in DsMrr_impl::get_disk_sweep_mrr_cost()

- Don't attempt to use BKA for materialized derived tables. The 
  table is neither filled nor fully opened yet, so attempt to 
  call handler->multi_range_read_info() causes crash.

mysql-test/r/derived_opt.result

@@ -352,4 +352,33 @@ pk	pk
 72	72
 80	80
 drop table t1, t2, t3, t4;
+#
+# MDEV-6879: Dereference of NULL primary_file->table in DsMrr_impl::get_disk_sweep_mrr_cost()
+#
+create table t1(a int);
+insert into t1 values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
+create table t2 (a int, b int, c text);
+insert into t2 
+select 
+A.a + B.a* 10,
+A.a + B.a* 10,
+'blob-data' 
+from t1 A, t1 B;
+set @tmp_jcl= @@join_cache_level;
+set @tmp_os= @@optimizer_switch;
+set join_cache_level=6;
+set @@optimizer_switch='derived_merge=on,derived_with_keys=on,mrr=on';
+explain 
+select * from 
+t1 join
+(select * from t2 order by a limit 1000) as D1 
+where 
+D1.a= t1.a;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	10	Using where
+1	PRIMARY	<derived2>	ref	key0	key0	5	test.t1.a	10	
+2	DERIVED	t2	ALL	NULL	NULL	NULL	NULL	100	Using filesort
+set join_cache_level=@tmp_jcl;
+set optimizer_switch=@tmp_os;
+drop table t1, t2;
 set optimizer_switch=@exit_optimizer_switch;

mysql-test/t/derived_opt.test

@@ -272,5 +272,34 @@ limit 10;
 
 drop table t1, t2, t3, t4;
 
+--echo #
+--echo # MDEV-6879: Dereference of NULL primary_file->table in DsMrr_impl::get_disk_sweep_mrr_cost()
+--echo #
+create table t1(a int);
+insert into t1 values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
+
+create table t2 (a int, b int, c text);
+insert into t2 
+select 
+  A.a + B.a* 10,
+  A.a + B.a* 10,
+  'blob-data' 
+from t1 A, t1 B;
+
+set @tmp_jcl= @@join_cache_level;
+set @tmp_os= @@optimizer_switch;
+set join_cache_level=6;
+set @@optimizer_switch='derived_merge=on,derived_with_keys=on,mrr=on';
+explain 
+select * from 
+  t1 join
+  (select * from t2 order by a limit 1000) as D1 
+where 
+  D1.a= t1.a;
+
+set join_cache_level=@tmp_jcl;
+set optimizer_switch=@tmp_os;
+drop table t1, t2;
+
 # The following command must be the last one the file 
 set optimizer_switch=@exit_optimizer_switch;

sql/sql_select.cc

@@ -10614,7 +10614,20 @@ uint check_join_cache_usage(JOIN_TAB *tab,
       goto no_join_cache;
     if (tab->ref.is_access_triggered())
       goto no_join_cache;
-      
+    
+    /*
+      Don't use BKA for materialized tables. We could actually have a
+      meaningful use of BKA when linked join buffers are used.
+
+      The problem is, the temp.table is not filled (actually not even opened
+      properly) yet, and this doesn't let us call 
+      handler->multi_range_read_info(). It is possible to come up with
+      estimates, etc. without acessing the table, but it seems not to worth the
+      effort now.
+    */
+    if (tab->table->pos_in_table_list->is_materialized_derived())
+      goto no_join_cache;
+
     if (!tab->is_ref_for_hash_join())
     {
       flags= HA_MRR_NO_NULL_ENDPOINTS | HA_MRR_SINGLE_POINT;