4 files changed, 108 insertions, 1 deletions
diff --git a/mysql-test/r/index_merge_myisam.result b/mysql-test/r/index_merge_myisam.result
index 091719095fb..0720dceac9a 100644
--- a/mysql-test/r/index_merge_myisam.result
+++ b/mysql-test/r/index_merge_myisam.result
@@ -1704,3 +1704,55 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t1	ALL	PRIMARY,c1,i,c2	NULL	NULL	NULL	69	Using where
 DROP TABLE t1;
 set optimizer_switch= @optimizer_switch_save;
+#
+# MDEV-21932: ROR union with index_merge_sort_union=off
+#
+create table t0 (a int);
+insert into t0 values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
+insert into t0 select a+10 from t0;
+insert into t0 select a+20 from t0;
+insert into t0 select a+40 from t0;
+insert into t0 select a+80 from t0;
+insert into t0 select a+160 from t0;
+delete from t0 where a > 300;
+create table t1 (
+f1 int, f2 int, f3 int, f4 int,
+primary key (f1),  key (f3),  key(f4)
+) engine=myisam;
+insert into t1 select a+100, a+100, a+100, a+100 from t0;
+insert into t1 VALUES (9,0,2,6), (9930,0,0,NULL);
+analyze table t1;
+Table	Op	Msg_type	Msg_text
+test.t1	analyze	status	OK
+set optimizer_switch='index_merge_sort_union=off';
+set optimizer_switch='index_merge_union=on';
+explain select * from t1
+where (( f3 = 1 or f1 = 7 )  and f1 < 10) or
+(f3 between 2 and 2 and ( f3 = 1 or f4 < 7 ));
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	index_merge	PRIMARY,f3,f4	f3,PRIMARY,f3	5,4,5	NULL	3	Using union(f3,PRIMARY,f3); Using where
+select * from t1
+where (( f3 = 1 or f1 = 7 )  and f1 < 10) or
+(f3 between 2 and 2 and ( f3 = 1 or f4 < 7 ));
+f1	f2	f3	f4
+9	0	2	6
+insert into t1 values (52,0,1,0),(53,0,1,0);
+insert into t1 values (50,0,1,0),(51,0,1,0);
+insert into t1 values (48,0,1,0),(49,0,1,0);
+insert into t1 values (46,0,1,0),(47,0,1,0);
+insert into t1 values (44,0,1,0),(45,0,1,0);
+analyze table t1;
+Table	Op	Msg_type	Msg_text
+test.t1	analyze	status	OK
+explain select * from t1
+where (( f3 = 1 or f1 = 7 )  and f1 < 10) or
+(f3 between 2 and 2 and ( f3 = 1 or f4 < 7 ));
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	index_merge	PRIMARY,f3,f4	f3,PRIMARY,f3	5,4,5	NULL	13	Using union(f3,PRIMARY,f3); Using where
+select * from t1
+where (( f3 = 1 or f1 = 7 )  and f1 < 10) or
+(f3 between 2 and 2 and ( f3 = 1 or f4 < 7 ));
+f1	f2	f3	f4
+9	0	2	6
+drop table t0,t1;
+set optimizer_switch= @optimizer_switch_save;
diff --git a/mysql-test/r/range_vs_index_merge.result b/mysql-test/r/range_vs_index_merge.result
index 0acaed37d22..752554ac53d 100644
--- a/mysql-test/r/range_vs_index_merge.result
+++ b/mysql-test/r/range_vs_index_merge.result
@@ -1653,7 +1653,7 @@ SELECT * FROM t1 FORCE KEY (PRIMARY,f3,f4)
 WHERE ( f3 = 1 OR f1 = 7 ) AND f1 < 10
 OR f3 BETWEEN 2 AND 2 AND ( f3 = 1 OR f4 != 1 );
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t1	ALL	PRIMARY,f3,f4	NULL	NULL	NULL	2	Using where
+1	SIMPLE	t1	index_merge	PRIMARY,f3,f4	f3,PRIMARY,f3	5,4,5	NULL	3	Using union(f3,PRIMARY,f3); Using where
 SELECT * FROM t1 FORCE KEY (PRIMARY,f3,f4)
 WHERE ( f3 = 1 OR f1 = 7 ) AND f1 < 10
 OR f3 BETWEEN 2 AND 2 AND ( f3 = 1 OR f4 != 1 );
diff --git a/mysql-test/t/index_merge_myisam.test b/mysql-test/t/index_merge_myisam.test
index 82d0474e28e..79aa5447215 100644
--- a/mysql-test/t/index_merge_myisam.test
+++ b/mysql-test/t/index_merge_myisam.test
@@ -243,3 +243,51 @@ DROP TABLE t1;
 
 set optimizer_switch= @optimizer_switch_save;
 
+--echo #
+--echo # MDEV-21932: ROR union with index_merge_sort_union=off
+--echo #
+
+create table t0 (a int);
+insert into t0 values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
+insert into t0 select a+10 from t0;
+insert into t0 select a+20 from t0;
+insert into t0 select a+40 from t0;
+insert into t0 select a+80 from t0;
+insert into t0 select a+160 from t0;
+delete from t0 where a > 300;
+
+create table t1 (
+  f1 int, f2 int, f3 int, f4 int,
+  primary key (f1),  key (f3),  key(f4)
+) engine=myisam;
+insert into t1 select a+100, a+100, a+100, a+100 from t0;
+insert into t1 VALUES (9,0,2,6), (9930,0,0,NULL);
+analyze table t1;
+
+set optimizer_switch='index_merge_sort_union=off';
+set optimizer_switch='index_merge_union=on';
+
+let $q1=
+select * from t1
+   where (( f3 = 1 or f1 = 7 )  and f1 < 10) or
+              (f3 between 2 and 2 and ( f3 = 1 or f4 < 7 ));
+eval explain $q1;
+eval $q1;
+
+insert into t1 values (52,0,1,0),(53,0,1,0);
+insert into t1 values (50,0,1,0),(51,0,1,0);
+insert into t1 values (48,0,1,0),(49,0,1,0);
+insert into t1 values (46,0,1,0),(47,0,1,0);
+insert into t1 values (44,0,1,0),(45,0,1,0);
+analyze table t1;
+
+let $q2=
+select * from t1
+   where (( f3 = 1 or f1 = 7 )  and f1 < 10) or
+              (f3 between 2 and 2 and ( f3 = 1 or f4 < 7 ));
+eval explain $q2;
+eval $q2;
+
+drop table t0,t1;
+
+set optimizer_switch= @optimizer_switch_save;
diff --git a/sql/opt_range.cc b/sql/opt_range.cc
index ca6f500fec6..70c1786dd83 100644
--- a/sql/opt_range.cc
+++ b/sql/opt_range.cc
@@ -6802,6 +6802,13 @@ static TRP_RANGE *get_key_scans_params(PARAM *param, SEL_TREE *tree,
                                         update_tbl_stats, &mrr_flags,
                                         &buf_size, &cost);
 
+      if (!param->is_ror_scan &&
+          !optimizer_flag(param->thd, OPTIMIZER_SWITCH_INDEX_MERGE_SORT_UNION))
+      {
+        /* The scan is not a ROR-scan, just skip it */
+        continue;
+      }
+
       if (found_records != HA_POS_ERROR && tree->index_scans &&
           (index_scan= (INDEX_SCAN_INFO *)alloc_root(param->mem_root,
 						     sizeof(INDEX_SCAN_INFO))))