MDEV-18679 Server crashes in JOIN::optimize

The bug manifested itself when executing a query with materialized
view/derived/CTE whose specification was a SELECT query contained
another materialized derived and impossible WHERE/HAVING condition
was detected for this SELECT.
As soon as such condition is detected the join structures of all
derived tables used in the SELECT are destroyed. So optimization
of the queries specifying these derived tables is impossible. Besides
it's not needed.

In 10.3 optimization of a materialized derived table is performed before
detection of impossible WHERE/HAVING condition in the embedding SELECT.

mysql-test/main/derived_cond_pushdown.result

@@ -16743,3 +16743,25 @@ id	username	id	userid	logindate
 set join_cache_level=default;
 DROP TABLE t1,t2;
 # End of 10.3 tests
+#
+# MDEV-18679: materialized view with SELECT S containing materialized
+#             derived when impossible WHERE has been detected for S
+#
+create table t1 (pk int, f varchar(1));
+insert into t1 values
+(3,'y'), (1,'x'), (7,'z');
+create view v1 as
+select t1.f
+from t1, (select distinct * from t1) t
+where t.f = t1.f and 1 = 0
+group by t1.f;
+select * from v1;
+f
+explain select * from v1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	<derived2>	system	NULL	NULL	NULL	NULL	0	Const row not found
+2	DERIVED	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE
+3	DERIVED	t1	ALL	NULL	NULL	NULL	NULL	3	Using temporary
+drop view v1;
+drop table t1;
+# End of 10.4 tests

mysql-test/main/derived_cond_pushdown.test

@@ -3263,3 +3263,26 @@ set join_cache_level=default;
 DROP TABLE t1,t2;
 
 --echo # End of 10.3 tests
+
+--echo #
+--echo # MDEV-18679: materialized view with SELECT S containing materialized
+--echo #             derived when impossible WHERE has been detected for S
+--echo #
+
+create table t1 (pk int, f varchar(1));
+insert into t1 values
+  (3,'y'), (1,'x'), (7,'z');
+
+create view v1 as
+select t1.f
+  from t1, (select distinct * from t1) t
+  where t.f = t1.f and 1 = 0
+group by t1.f;
+
+select * from v1;
+explain select * from v1;
+
+drop view v1;
+drop table t1;
+
+--echo # End of 10.4 tests

sql/sql_derived.cc

@@ -1002,6 +1002,15 @@ bool mysql_derived_optimize(THD *thd, LEX *lex, TABLE_LIST *derived)
         if (unit->optimized)
           DBUG_RETURN(FALSE);        
 	unit->optimized= TRUE;
+        if (!join)
+	{
+          /*
+            This happens when derived is used in SELECT for which
+            zer_result_cause != 0.
+            In this case join is already destroyed.
+	  */
+          DBUG_RETURN(FALSE);
+        }
       }
       if ((res= join->optimize()))
         goto err;