MDEV-24767 Wrong result when forced BNLH is used for join supported

           by compound index

This typo bug may lead to wrong result sets for equi-join queries where
the join operation is supported by a compound index such that the order of
its components differs from the order of the corresponding columns in
the table the index belongs to. The bug manifests itself only when usage
of the BNLH algorithm is forced.

The fix for the bug was provided by Chu Huaxing.

mysql-test/r/join_cache.result

@@ -6107,4 +6107,34 @@ WHERE e IS NULL;
 a	b	c	d	e
 DROP TABLE t1,t2,t3,t4;
 set join_cache_level=@save_join_cache_level;
+#
+# MDEV-24767: forced BNLH used for equi-join supported by compound index
+#
+create table t1 (a int, b int, c int ) engine=myisam ;
+create table t2 (a int, b int, c int, primary key (c,a,b)) engine=myisam ;
+insert into t1 values (3,4,2), (5,6,4);
+insert into t2 values (3,4,2), (5,6,4);
+select t1.a, t1.b, t1.c from t1,t2
+where t2.a = t1.a and t2.b = t1.b and t2.c=t1.c;
+a	b	c
+3	4	2
+5	6	4
+explain select t1.a, t1.b, t1.c from t1,t2
+where t2.a = t1.a and t2.b = t1.b and t2.c=t1.c;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	2	Using where
+1	SIMPLE	t2	eq_ref	PRIMARY	PRIMARY	12	test.t1.c,test.t1.a,test.t1.b	1	Using index
+set join_cache_level=3;
+select t1.a, t1.b, t1.c from t1,t2
+where t2.a = t1.a and t2.b = t1.b and t2.c=t1.c;
+a	b	c
+3	4	2
+5	6	4
+explain select t1.a, t1.b, t1.c from t1,t2
+where t2.a = t1.a and t2.b = t1.b and t2.c=t1.c;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	2	Using where
+1	SIMPLE	t2	hash_index	PRIMARY	#hash#PRIMARY:PRIMARY	12:12	test.t1.c,test.t1.a,test.t1.b	2	Using index; Using join buffer (flat, BNLH join)
+drop table t1,t2;
+set join_cache_level=@save_join_cache_level;
 set @@optimizer_switch=@save_optimizer_switch;

mysql-test/t/join_cache.test

@@ -4050,5 +4050,29 @@ DROP TABLE t1,t2,t3,t4;
 
 set join_cache_level=@save_join_cache_level;
 
+--echo #
+--echo # MDEV-24767: forced BNLH used for equi-join supported by compound index
+--echo #
+
+create table t1 (a int, b int, c int ) engine=myisam ;
+create table t2 (a int, b int, c int, primary key (c,a,b)) engine=myisam ;
+insert into t1 values (3,4,2), (5,6,4);
+insert into t2 values (3,4,2), (5,6,4);
+
+let $q=
+select t1.a, t1.b, t1.c from t1,t2
+  where t2.a = t1.a and t2.b = t1.b and t2.c=t1.c;
+
+eval $q;
+eval explain $q;
+
+set join_cache_level=3;
+eval $q;
+eval explain $q;
+
+drop table t1,t2;
+
+set join_cache_level=@save_join_cache_level;
+
 # The following command must be the last one in the file 
 set @@optimizer_switch=@save_optimizer_switch;

sql/sql_join_cache.cc

@@ -1199,7 +1199,7 @@ bool JOIN_CACHE::check_emb_key_usage()
     Item *item= ref->items[i]->real_item();
     Field *fld= ((Item_field *) item)->field;
     CACHE_FIELD *init_copy= field_descr+flag_fields+i; 
-    for (j= i, copy= init_copy; i < local_key_arg_fields;  i++, copy++)
+    for (j= i, copy= init_copy; j < local_key_arg_fields;  j++, copy++)
     {
       if (fld->eq(copy->field))
       {