MDEV-18467 Server crashes in fix_semijoin_strategies_for_picked_join_order

If a splittable materialized derived table / view T is used in a inner nest
of an outer join with impossible ON condition then T is marked as a
constant table. Yet the execution plan to build T is still searched for
in spite of the fact that is not needed. So it should be set.

mysql-test/main/derived_split_innodb.result

@@ -99,3 +99,44 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 2	LATERAL DERIVED	t1	eq_ref	PRIMARY	PRIMARY	4	test.t2.id	1	
 set join_cache_level=default;
 DROP TABLE t1,t2;
+#
+# Bug mdev-18467: join of grouping view and a base table as inner operand
+#                 of left join with on condition containing impossible range
+#
+create table t1 (f1 int, f2 int, key(f2)) engine=InnoDB;
+insert into t1 values (3,33), (7,77), (1,11);
+create table t2 (f1 int, f2 int, primary key (f1)) engine=InnoDB;
+insert into t2 values (3,33), (9,99), (1,11);
+create view v1 as
+select f1, max(f2) as f2 from t2 group by f1;
+select t.f2
+from t1
+left join
+(v1 join t1 as t on v1.f1=t.f1 and t.f2 = null)
+on t1.f1=t.f1;
+f2
+NULL
+NULL
+NULL
+explain select t.f2
+from t1
+left join
+(v1 join t1 as t on v1.f1=t.f1 and t.f2 = null)
+on t1.f1=t.f1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t	const	f2	NULL	NULL	NULL	1	Impossible ON condition
+1	PRIMARY	<derived2>	const	key1	NULL	NULL	NULL	1	Impossible ON condition
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	
+2	DERIVED	t2	ALL	PRIMARY	NULL	NULL	NULL	3	Using temporary; Using filesort
+set statement optimizer_switch='split_materialized=off' for explain select t.f2
+from t1
+left join
+(v1 join t1 as t on v1.f1=t.f1 and t.f2 = null)
+on t1.f1=t.f1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t	const	f2	NULL	NULL	NULL	1	Impossible ON condition
+1	PRIMARY	<derived2>	const	key1	NULL	NULL	NULL	1	Impossible ON condition
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	
+2	DERIVED	t2	index	NULL	PRIMARY	4	NULL	3	
+drop view v1;
+drop table t1,t2;

mysql-test/main/derived_split_innodb.test

@@ -94,3 +94,32 @@ eval EXPLAIN $q;
 set join_cache_level=default;
 
 DROP TABLE t1,t2;
+
+--echo #
+--echo # Bug mdev-18467: join of grouping view and a base table as inner operand
+--echo #                 of left join with on condition containing impossible range
+--echo #
+
+create table t1 (f1 int, f2 int, key(f2)) engine=InnoDB;
+insert into t1 values (3,33), (7,77), (1,11);
+
+create table t2 (f1 int, f2 int, primary key (f1)) engine=InnoDB;
+insert into t2 values (3,33), (9,99), (1,11);
+
+create view v1 as
+  select f1, max(f2) as f2 from t2 group by f1;
+
+let $q=
+select t.f2
+  from t1
+       left join
+       (v1 join t1 as t on v1.f1=t.f1 and t.f2 = null)
+       on t1.f1=t.f1;
+
+eval $q;
+eval explain $q;
+eval set statement optimizer_switch='split_materialized=off' for explain $q;
+
+drop view v1;
+
+drop table t1,t2;

sql/opt_split.cc

@@ -1078,6 +1078,7 @@ bool JOIN::inject_best_splitting_cond(table_map remaining_tables)
   @param
     spl_plan   info on the splitting plan chosen for the splittable table T
     remaining_tables  the table T is joined just before these tables
+    is_const_table    the table T is a constant table
 
   @details
     If in the final query plan the optimizer has chosen a splitting plan
@@ -1091,12 +1092,13 @@ bool JOIN::inject_best_splitting_cond(table_map remaining_tables)
 */
 
 bool JOIN_TAB::fix_splitting(SplM_plan_info *spl_plan,
-                             table_map remaining_tables)
+                             table_map remaining_tables,
+                             bool is_const_table)
 {
   SplM_opt_info *spl_opt_info= table->spl_opt_info;
   DBUG_ASSERT(table->spl_opt_info != 0);
   JOIN *md_join= spl_opt_info->join;
-  if (spl_plan)
+  if (spl_plan && !is_const_table)
   {
     memcpy((char *) md_join->best_positions,
            (char *) spl_plan->best_positions,
@@ -1113,7 +1115,7 @@ bool JOIN_TAB::fix_splitting(SplM_plan_info *spl_plan,
                                     remaining_tables,
                                     true);
   }
-  else
+  else if (md_join->save_qep)
   {
     md_join->restore_query_plan(md_join->save_qep);
   }
@@ -1143,10 +1145,11 @@ bool JOIN::fix_all_splittings_in_plan()
   {
     POSITION *cur_pos= &best_positions[tablenr];
     JOIN_TAB *tab= cur_pos->table;
-    if (tablenr >= const_tables && tab->table->is_splittable())
+    if (tab->table->is_splittable())
     {
       SplM_plan_info *spl_plan= cur_pos->spl_plan;
-      if (tab->fix_splitting(spl_plan, all_tables & ~prev_tables))
+      if (tab->fix_splitting(spl_plan, all_tables & ~prev_tables,
+                             tablenr < const_tables ))
           return true;
     }
     prev_tables|= tab->table->map;

sql/sql_select.cc

@@ -6689,6 +6689,7 @@ void set_position(JOIN *join,uint idx,JOIN_TAB *table,KEYUSE *key)
     next=tmp;
   }
   join->best_ref[idx]=table;
+  join->positions[idx].spl_plan= 0;
 }
 
 

sql/sql_select.h

@@ -659,7 +659,8 @@ typedef struct st_join_table {
   void add_keyuses_for_splitting();
   SplM_plan_info *choose_best_splitting(double record_count,
                                         table_map remaining_tables);
-  bool fix_splitting(SplM_plan_info *spl_plan, table_map remaining_tables);
+  bool fix_splitting(SplM_plan_info *spl_plan, table_map remaining_tables,
+                     bool is_const_table);
 } JOIN_TAB;