MDEV-26938 Support descending indexes internally in InnoDB (server part)

* preserve DESC index property in the parser
* store it in the frm (only for HA_KEY_ALG_BTREE)
* read it from the frm
* show it in SHOW CREATE
* skip DESC indexes in opt_range.cc and opt_sum.cc
* ORDER BY test

This includes a fix of MDEV-27432.

mysql-test/main/func_group.result

@@ -318,7 +318,7 @@ a3 char(3),
 a4 real,
 a5 date,
 key k1(a2,a3),
-key k2(a4 desc,a1),
+key k2(a4 /*desc*/,a1),
 key k3(a5,a1)
 );
 create table t2(

mysql-test/main/func_group.test

@@ -206,7 +206,7 @@ create table t1(
   a4 real,
   a5 date,
   key k1(a2,a3),
-  key k2(a4 desc,a1),
+  key k2(a4 /*desc*/,a1),
   key k3(a5,a1)
 );
 create table t2(

mysql-test/main/key.result

@@ -1,4 +1,3 @@
-drop table if exists t1,t2,t3;
 SET SQL_WARNINGS=1;
 CREATE TABLE t1 (
 ID CHAR(32) NOT NULL,
@@ -685,3 +684,8 @@ c	c
 9	10
 10	11
 drop table t1,t2;
+#
+# MDEV-13756 Implement descending index: KEY (a DESC, b ASC)
+#
+create table t1 (a int, b int, key(a), key(a desc));
+drop table t1;

mysql-test/main/key.test

@@ -1,6 +1,3 @@
---disable_warnings
-drop table if exists t1,t2,t3;
---enable_warnings
 --source include/have_sequence.inc
 SET SQL_WARNINGS=1;
 
@@ -603,3 +600,9 @@ EXPLAIN SELECT t1.c, t2.c FROM t1, t2 WHERE t1.b=t2.a and t1.c=t2.b;
 SELECT t1.c, t2.c FROM t1, t2 WHERE t1.b=t2.a and t1.c=t2.b;
 
 drop table t1,t2;
+
+--echo #
+--echo # MDEV-13756 Implement descending index: KEY (a DESC, b ASC)
+--echo #
+create table t1 (a int, b int, key(a), key(a desc));
+drop table t1;

mysql-test/main/opt_trace.result

@@ -1201,8 +1201,8 @@ EXPLAIN SELECT DISTINCT a FROM t1	{
                     },
                     {
                       "index": "a",
-                      "usable": true,
+                      "key_parts": ["a"],
-                      "key_parts": ["a"]
+                      "usable": true
                     }
                   ],
                   "best_covering_index_scan": {
@@ -1384,8 +1384,8 @@ EXPLAIN SELECT MIN(d) FROM t1 where b=2 and c=3  group by a	{
                   "potential_range_indexes": [
                     {
                       "index": "a",
-                      "usable": true,
+                      "key_parts": ["a", "b", "c", "d"],
-                      "key_parts": ["a", "b", "c", "d"]
+                      "usable": true
                     }
                   ],
                   "best_covering_index_scan": {
@@ -1583,8 +1583,8 @@ EXPLAIN SELECT id,MIN(a),MAX(a) FROM t1 WHERE a>=20010104e0 GROUP BY id	{
                   "potential_range_indexes": [
                     {
                       "index": "id",
-                      "usable": true,
+                      "key_parts": ["id", "a"],
-                      "key_parts": ["id", "a"]
+                      "usable": true
                     }
                   ],
                   "best_covering_index_scan": {
@@ -1771,8 +1771,8 @@ EXPLAIN SELECT * FROM t1 WHERE a = 20010104e0 GROUP BY id	{
                   "potential_range_indexes": [
                     {
                       "index": "id",
-                      "usable": true,
+                      "key_parts": ["id", "a"],
-                      "key_parts": ["id", "a"]
+                      "usable": true
                     }
                   ],
                   "best_covering_index_scan": {
@@ -2010,13 +2010,13 @@ explain  select * from t1 where a=1 and b=2 order by c limit 1	{
                     },
                     {
                       "index": "a_c",
-                      "usable": true,
+                      "key_parts": ["a", "c"],
-                      "key_parts": ["a", "c"]
+                      "usable": true
                     },
                     {
                       "index": "a_b",
-                      "usable": true,
+                      "key_parts": ["a", "b"],
-                      "key_parts": ["a", "b"]
+                      "usable": true
                     }
                   ],
                   "setup_range_conditions": [],
@@ -2213,8 +2213,8 @@ explain  select * from t1 where a=1 and b=2 order by c limit 1	{
                 },
                 {
                   "index": "a_c",
-                  "usable": true,
+                  "key_parts": ["a", "c"],
-                  "key_parts": ["a", "c"]
+                  "usable": true
                 },
                 {
                   "index": "a_b",
@@ -3233,18 +3233,18 @@ explain select * from t1 where pk = 2 and a=5 and b=1	{
                   "potential_range_indexes": [
                     {
                       "index": "pk",
-                      "usable": true,
+                      "key_parts": ["pk"],
-                      "key_parts": ["pk"]
+                      "usable": true
                     },
                     {
                       "index": "pk_a",
-                      "usable": true,
+                      "key_parts": ["pk", "a"],
-                      "key_parts": ["pk", "a"]
+                      "usable": true
                     },
                     {
                       "index": "pk_a_b",
-                      "usable": true,
+                      "key_parts": ["pk", "a", "b"],
-                      "key_parts": ["pk", "a", "b"]
+                      "usable": true
                     }
                   ],
                   "best_covering_index_scan": {
@@ -3751,8 +3751,8 @@ explain delete from t0 where t0.a<3	{
         "potential_range_indexes": [
           {
             "index": "a",
-            "usable": true,
+            "key_parts": ["a"],
-            "key_parts": ["a"]
+            "usable": true
           }
         ],
         "setup_range_conditions": [],
@@ -3889,8 +3889,8 @@ explain delete t0,t1 from t0, t1 where t0.a=t1.a and t1.a<3	{
                   "potential_range_indexes": [
                     {
                       "index": "a",
-                      "usable": true,
+                      "key_parts": ["a"],
-                      "key_parts": ["a"]
+                      "usable": true
                     }
                   ],
                   "best_covering_index_scan": {
@@ -3954,8 +3954,8 @@ explain delete t0,t1 from t0, t1 where t0.a=t1.a and t1.a<3	{
                   "potential_range_indexes": [
                     {
                       "index": "a",
-                      "usable": true,
+                      "key_parts": ["a"],
-                      "key_parts": ["a"]
+                      "usable": true
                     }
                   ],
                   "best_covering_index_scan": {

mysql-test/main/opt_trace_index_merge.result

@@ -78,13 +78,13 @@ explain select * from t1 where a=1 or b=1	{
                   "potential_range_indexes": [
                     {
                       "index": "a",
-                      "usable": true,
+                      "key_parts": ["a"],
-                      "key_parts": ["a"]
+                      "usable": true
                     },
                     {
                       "index": "b",
-                      "usable": true,
+                      "key_parts": ["b"],
-                      "key_parts": ["b"]
+                      "usable": true
                     },
                     {
                       "index": "c",

mysql-test/main/opt_trace_index_merge_innodb.result

@@ -93,13 +93,13 @@ explain select * from t1 where pk1 != 0  and key1 = 1	{
                   "potential_range_indexes": [
                     {
                       "index": "PRIMARY",
-                      "usable": true,
+                      "key_parts": ["pk1", "pk2"],
-                      "key_parts": ["pk1", "pk2"]
+                      "usable": true
                     },
                     {
                       "index": "key1",
-                      "usable": true,
+                      "key_parts": ["key1"],
-                      "key_parts": ["key1"]
+                      "usable": true
                     },
                     {
                       "index": "key2",

mysql-test/main/order_by.result

@@ -1,5 +1,4 @@
 call mtr.add_suppression("Sort aborted.*");
-drop table if exists t1,t2,t3;
 call mtr.add_suppression("Out of sort memory; increase server sort buffer size");
 CREATE TABLE t1 (
 id int(6) DEFAULT '0' NOT NULL,
@@ -4487,3 +4486,38 @@ a	group_concat(t1.b)
 58	1
 DROP TABLE t1, t2;
 # End of 10.6 tests
+#
+# MDEV-13756 Implement descending index: KEY (a DESC, b ASC)
+#
+create table t1 (a int, b int, c int, key r (a desc, b asc));
+insert t1 select seq % 10, seq div 10, seq from seq_1_to_55;
+insert t1 values (NULL, NULL, NULL), (9, NULL, NULL);
+explain select * from t1 force index(r) order by a,b limit 20;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	57	Using filesort
+explain select * from t1 force index(r) order by a desc,b limit 20;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	index	NULL	r	10	NULL	20	
+select * from t1 force index(r) order by a desc,b limit 20;
+a	b	c
+9	NULL	NULL
+9	0	9
+9	1	19
+9	2	29
+9	3	39
+9	4	49
+8	0	8
+8	1	18
+8	2	28
+8	3	38
+8	4	48
+7	0	7
+7	1	17
+7	2	27
+7	3	37
+7	4	47
+6	0	6
+6	1	16
+6	2	26
+6	3	36
+drop table t1;

mysql-test/main/order_by.test

@@ -3,11 +3,6 @@
 #
 
 call mtr.add_suppression("Sort aborted.*");
-
---disable_warnings
-drop table if exists t1,t2,t3;
---enable_warnings
-
 call mtr.add_suppression("Out of sort memory; increase server sort buffer size");
 --source include/have_sequence.inc
 
@@ -15,8 +10,6 @@ call mtr.add_suppression("Out of sort memory; increase server sort buffer size")
 # Test old ORDER BY bug
 #
 
---source include/have_sequence.inc
-
 CREATE TABLE t1 (
   id int(6) DEFAULT '0' NOT NULL,
   idservice int(5),
@@ -2649,3 +2642,14 @@ eval $query;
 DROP TABLE t1, t2;
 
 --echo # End of 10.6 tests
+
+--echo #
+--echo # MDEV-13756 Implement descending index: KEY (a DESC, b ASC)
+--echo #
+create table t1 (a int, b int, c int, key r (a desc, b asc));
+insert t1 select seq % 10, seq div 10, seq from seq_1_to_55;
+insert t1 values (NULL, NULL, NULL), (9, NULL, NULL);
+explain select * from t1 force index(r) order by a,b limit 20;
+explain select * from t1 force index(r) order by a desc,b limit 20;
+        select * from t1 force index(r) order by a desc,b limit 20;
+drop table t1;

mysql-test/main/order_by_innodb.result

@@ -220,6 +220,41 @@ dd.d1, dd.d2, dd.id limit 1
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	index	NULL	PRIMARY	4	NULL	#	Using index
 1	PRIMARY	t2	eq_ref	PRIMARY,id2	PRIMARY	4	func	#	Using where
-2	DEPENDENT SUBQUERY	dd	range	id2,for_latest_sort	for_latest_sort	6	NULL	#	Using where
+2	DEPENDENT SUBQUERY	dd	index	id2,for_latest_sort	for_latest_sort	14	NULL	#	Using where
 drop table t1,t2;
 # End of 10.2 tests
+#
+# MDEV-26938 Support descending indexes internally in InnoDB
+#
+create table t1 (a int, b int, c int, key r (a desc, b asc));
+insert t1 select seq % 10, seq div 10, seq from seq_1_to_55;
+insert t1 values (NULL, NULL, NULL), (9, NULL, NULL);
+explain select * from t1 force index(r) order by a,b limit 20;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	57	Using filesort
+explain select * from t1 force index(r) order by a desc,b limit 20;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	index	NULL	r	10	NULL	20	
+select * from t1 force index(r) order by a desc,b limit 20;
+a	b	c
+9	NULL	NULL
+9	0	9
+9	1	19
+9	2	29
+9	3	39
+9	4	49
+8	0	8
+8	1	18
+8	2	28
+8	3	38
+8	4	48
+7	0	7
+7	1	17
+7	2	27
+7	3	37
+7	4	47
+6	0	6
+6	1	16
+6	2	26
+6	3	36
+drop table t1;

mysql-test/main/order_by_innodb.test

@@ -1,7 +1,8 @@
 #
 # ORDER BY handling (e.g. filesort) tests that require innodb
 #
--- source include/have_innodb.inc
+--source include/have_innodb.inc
+--source include/have_sequence.inc
 
 --disable_warnings
 drop table if exists t0,t1,t2,t3;
@@ -209,3 +210,14 @@ from
 drop table t1,t2;
 
 --echo # End of 10.2 tests
+
+--echo #
+--echo # MDEV-26938 Support descending indexes internally in InnoDB
+--echo #
+create table t1 (a int, b int, c int, key r (a desc, b asc));
+insert t1 select seq % 10, seq div 10, seq from seq_1_to_55;
+insert t1 values (NULL, NULL, NULL), (9, NULL, NULL);
+explain select * from t1 force index(r) order by a,b limit 20;
+explain select * from t1 force index(r) order by a desc,b limit 20;
+        select * from t1 force index(r) order by a desc,b limit 20;
+drop table t1;

mysql-test/main/partition_order.result

@@ -1,4 +1,3 @@
-drop table if exists t1;
 CREATE TABLE t1 (
 a int not null,
 b int not null,
@@ -783,3 +782,17 @@ a	b	c
 1	1	1
 1	NULL	NULL
 drop table t1;
+#
+# MDEV-13756 Implement descending index: KEY (a DESC, b ASC)
+#
+create table t1 (a int, b int, key(a desc)) partition by hash(a) partitions 4;
+insert into t1 values (1,1),(2,2),(3,3),(4,4),(5,5),(6,6);
+explain select * from t1 order by a limit 3;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	index	NULL	a	5	NULL	3	
+select * from t1 order by a limit 3;
+a	b
+1	1
+2	2
+3	3
+drop table t1;

mysql-test/main/partition_order.test

@@ -1,14 +1,9 @@
-#--disable_abort_on_error
 #
 # Simple test for the partition storage engine
 # Focuses on tests of ordered index read
 # 
 -- source include/have_partition.inc
 
---disable_warnings
-drop table if exists t1;
---enable_warnings
-
 #
 # Ordered index read, int type
 #
@@ -842,3 +837,12 @@ INSERT into t1 values (1, NULL, NULL), (2, NULL, '10');
 select * from t1 where a = 1 order by a desc, b desc;
 select * from t1 where a = 1 order by b desc;
 drop table t1;
+
+--echo #
+--echo # MDEV-13756 Implement descending index: KEY (a DESC, b ASC)
+--echo #
+create table t1 (a int, b int, key(a desc)) partition by hash(a) partitions 4;
+insert into t1 values (1,1),(2,2),(3,3),(4,4),(5,5),(6,6);
+explain select * from t1 order by a limit 3;
+select * from t1 order by a limit 3;
+drop table t1;

mysql-test/main/type_timestamp.result

@@ -575,7 +575,7 @@ a
 2010-02-01 09:31:02
 2010-02-01 09:31:03
 2010-02-01 09:31:04
-CREATE TABLE t2 ( a TIMESTAMP, KEY ( a DESC ) );
+CREATE TABLE t2 ( a TIMESTAMP, KEY ( a ) );
 INSERT INTO t2 VALUES( '2010-02-01 09:31:01' );
 INSERT INTO t2 VALUES( '2010-02-01 09:31:02' );
 INSERT INTO t2 VALUES( '2010-02-01 09:31:03' );

mysql-test/main/type_timestamp.test

@@ -386,7 +386,7 @@ EXPLAIN
 SELECT * FROM t1 WHERE a >= '2010-02-01 09:31:02.0';
 SELECT * FROM t1 WHERE a >= '2010-02-01 09:31:02.0';
 
-CREATE TABLE t2 ( a TIMESTAMP, KEY ( a DESC ) );
+CREATE TABLE t2 ( a TIMESTAMP, KEY ( a ) );
 
 INSERT INTO t2 VALUES( '2010-02-01 09:31:01' );
 INSERT INTO t2 VALUES( '2010-02-01 09:31:02' );

mysql-test/suite/innodb/r/autoinc_persist,desc.rdiff

@@ -1,4 +1,4 @@
-@@ -13,7 +13,7 @@
+@@ -13,212 +13,212 @@
  #
  # Pre-create several tables
  SET SQL_MODE='STRICT_ALL_TABLES';
@@ -7,106 +7,347 @@
  INSERT INTO t1 VALUES(0), (0), (0), (0), (-1), (-10), (0),
  (20), (30), (31);
  SELECT * FROM t1;
-@@ -28,7 +28,7 @@
+ a
- 20
+--10
- 30
+--1
+-1
+-2
+-3
+-4
+-5
+-20
+-30
  31
 -CREATE TABLE t2(a TINYINT UNSIGNED AUTO_INCREMENT KEY) ENGINE = InnoDB;
++30
++20
++5
++4
++3
++2
++1
++-1
++-10
 +CREATE TABLE t2(a TINYINT UNSIGNED AUTO_INCREMENT, PRIMARY KEY(a DESC)) ENGINE = InnoDB;
  INSERT INTO t2 VALUES(-5);
  ERROR 22003: Out of range value for column 'a' at row 1
  INSERT INTO t2 VALUES(0), (0), (0), (0), (8), (10), (0),
-@@ -45,7 +45,7 @@
+ (20), (30), (31);
- 20
+ SELECT * FROM t2;
- 30
+ a
+-1
+-2
+-3
+-4
+-8
+-10
+-11
+-20
+-30
  31
 -CREATE TABLE t3(a SMALLINT AUTO_INCREMENT KEY) ENGINE = InnoDB;
++30
++20
++11
++10
++8
++4
++3
++2
++1
 +CREATE TABLE t3(a SMALLINT AUTO_INCREMENT, PRIMARY KEY(a DESC)) ENGINE = InnoDB;
  INSERT INTO t3 VALUES(0), (0), (0), (0), (-1), (-10), (0),
  (20), (30), (31), (1024), (4096);
  SELECT * FROM t3;
-@@ -62,7 +62,7 @@
+ a
- 31
+--10
- 1024
+--1
+-1
+-2
+-3
+-4
+-5
+-20
+-30
+-31
+-1024
  4096
 -CREATE TABLE t4(a SMALLINT UNSIGNED AUTO_INCREMENT KEY) ENGINE = InnoDB;
++1024
++31
++30
++20
++5
++4
++3
++2
++1
++-1
++-10
 +CREATE TABLE t4(a SMALLINT UNSIGNED AUTO_INCREMENT, PRIMARY KEY(a DESC)) ENGINE = InnoDB;
  INSERT INTO t4 VALUES(-5);
  ERROR 22003: Out of range value for column 'a' at row 1
  INSERT INTO t4 VALUES(0), (0), (0), (0), (8), (10), (0),
-@@ -81,7 +81,7 @@
+ (20), (30), (31), (1024), (4096);
- 31
+ SELECT * FROM t4;
- 1024
+ a
+-1
+-2
+-3
+-4
+-8
+-10
+-11
+-20
+-30
+-31
+-1024
  4096
 -CREATE TABLE t5(a MEDIUMINT AUTO_INCREMENT KEY) ENGINE = InnoDB;
++1024
++31
++30
++20
++11
++10
++8
++4
++3
++2
++1
 +CREATE TABLE t5(a MEDIUMINT AUTO_INCREMENT, PRIMARY KEY(a DESC)) ENGINE = InnoDB;
  INSERT INTO t5 VALUES(0), (0), (0), (0), (-1), (-10), (0),
  (20), (30), (31), (1000000), (1000005);
  SELECT * FROM t5;
-@@ -98,7 +98,7 @@
+ a
- 31
+--10
- 1000000
+--1
+-1
+-2
+-3
+-4
+-5
+-20
+-30
+-31
+-1000000
  1000005
 -CREATE TABLE t6(a MEDIUMINT UNSIGNED AUTO_INCREMENT KEY) ENGINE = InnoDB;
++1000000
++31
++30
++20
++5
++4
++3
++2
++1
++-1
++-10
 +CREATE TABLE t6(a MEDIUMINT UNSIGNED AUTO_INCREMENT, PRIMARY KEY(a DESC)) ENGINE = InnoDB;
  INSERT INTO t6 VALUES(-5);
  ERROR 22003: Out of range value for column 'a' at row 1
  INSERT INTO t6 VALUES(0), (0), (0), (0), (8), (10), (0),
-@@ -117,7 +117,7 @@
+ (20), (30), (31), (1000000), (1000005);
- 31
+ SELECT * FROM t6;
- 1000000
+ a
+-1
+-2
+-3
+-4
+-8
+-10
+-11
+-20
+-30
+-31
+-1000000
  1000005
 -CREATE TABLE t7(a INT AUTO_INCREMENT KEY) ENGINE = InnoDB;
++1000000
++31
++30
++20
++11
++10
++8
++4
++3
++2
++1
 +CREATE TABLE t7(a INT AUTO_INCREMENT, PRIMARY KEY(a DESC)) ENGINE = InnoDB;
  INSERT INTO t7 VALUES(0), (0), (0), (0), (-1), (-10), (0),
  (20), (30), (31), (100000000), (100000008);
  SELECT * FROM t7;
-@@ -134,7 +134,7 @@
+ a
- 31
+--10
- 100000000
+--1
+-1
+-2
+-3
+-4
+-5
+-20
+-30
+-31
+-100000000
  100000008
 -CREATE TABLE t8(a INT UNSIGNED AUTO_INCREMENT KEY) ENGINE = InnoDB;
++100000000
++31
++30
++20
++5
++4
++3
++2
++1
++-1
++-10
 +CREATE TABLE t8(a INT UNSIGNED AUTO_INCREMENT, PRIMARY KEY(a DESC)) ENGINE = InnoDB;
  INSERT INTO t8 VALUES(-5);
  ERROR 22003: Out of range value for column 'a' at row 1
  INSERT INTO t8 VALUES(0), (0), (0), (0), (8), (10), (0),
-@@ -153,7 +153,7 @@
+ (20), (30), (31), (100000000), (100000008);
- 31
+ SELECT * FROM t8;
- 100000000
+ a
+-1
+-2
+-3
+-4
+-8
+-10
+-11
+-20
+-30
+-31
+-100000000
  100000008
 -CREATE TABLE t9(a BIGINT AUTO_INCREMENT KEY) ENGINE = InnoDB;
++100000000
++31
++30
++20
++11
++10
++8
++4
++3
++2
++1
 +CREATE TABLE t9(a BIGINT AUTO_INCREMENT, PRIMARY KEY(a DESC)) ENGINE = InnoDB;
  INSERT INTO t9 VALUES(0), (0), (0), (0), (-1), (-10), (0),
  (20), (30), (31), (100000000000), (100000000006);
  SELECT * FROM t9;
-@@ -170,7 +170,7 @@
+ a
- 31
+--10
- 100000000000
+--1
+-1
+-2
+-3
+-4
+-5
+-20
+-30
+-31
+-100000000000
  100000000006
 -CREATE TABLE t10(a BIGINT UNSIGNED AUTO_INCREMENT KEY) ENGINE = InnoDB;
++100000000000
++31
++30
++20
++5
++4
++3
++2
++1
++-1
++-10
 +CREATE TABLE t10(a BIGINT UNSIGNED AUTO_INCREMENT, PRIMARY KEY(a DESC)) ENGINE = InnoDB;
  INSERT INTO t10 VALUES(-5);
  ERROR 22003: Out of range value for column 'a' at row 1
  INSERT INTO t10 VALUES(0), (0), (0), (0), (8), (10), (0),
-@@ -189,7 +189,7 @@
+ (20), (30), (31), (100000000000), (100000000006);
- 31
+ SELECT * FROM t10;
- 100000000000
+ a
+-1
+-2
+-3
+-4
+-8
+-10
+-11
+-20
+-30
+-31
+-100000000000
  100000000006
 -CREATE TABLE t11(a FLOAT AUTO_INCREMENT KEY) ENGINE = InnoDB;
++100000000000
++31
++30
++20
++11
++10
++8
++4
++3
++2
++1
 +CREATE TABLE t11(a FLOAT AUTO_INCREMENT, PRIMARY KEY(a DESC)) ENGINE = InnoDB;
  INSERT INTO t11 VALUES(0), (0), (0), (0), (-1), (-10), (0),
  (20), (30), (31);
  SELECT * FROM t11;
-@@ -204,7 +204,7 @@
+ a
- 20
+--10
- 30
+--1
+-1
+-2
+-3
+-4
+-5
+-20
+-30
  31
 -CREATE TABLE t12(a DOUBLE AUTO_INCREMENT KEY) ENGINE = InnoDB;
++30
++20
++5
++4
++3
++2
++1
++-1
++-10
 +CREATE TABLE t12(a DOUBLE AUTO_INCREMENT, PRIMARY KEY(a DESC)) ENGINE = InnoDB;
  INSERT INTO t12 VALUES(0), (0), (0), (0), (-1), (-10), (0),
  (20), (30), (31);
  SELECT * FROM t12;
-@@ -242,7 +242,7 @@
+ a
+--10
+--1
+-1
+-2
+-3
+-4
+-5
+-20
+-30
+ 31
++30
++20
++5
++4
++3
++2
++1
++-1
++-10
+ # Scenario 1: Normal restart, to test if the counters are persisted
+ # Scenario 2: Delete some values, to test the counters should not be the
+ # one which is the largest in current table
+@@ -242,14 +242,14 @@
  SELECT MAX(a) AS `Expect 100000000000` FROM t9;
  Expect 100000000000
  100000000000
@@ -115,6 +356,333 @@
  AUTO_INCREMENT = 1234;
  # restart
  SHOW CREATE TABLE t13;
+ Table	Create Table
+ t13	CREATE TABLE `t13` (
+   `a` int(11) NOT NULL AUTO_INCREMENT,
+-  PRIMARY KEY (`a`)
++  PRIMARY KEY (`a` DESC)
+ ) ENGINE=InnoDB AUTO_INCREMENT=1234 DEFAULT CHARSET=latin1
+ INSERT INTO t13 VALUES(0);
+ SELECT a AS `Expect 1234` FROM t13;
+@@ -464,28 +464,28 @@
+ INSERT INTO t1 VALUES(0), (0);
+ SELECT * FROM t1;
+ a
+-1
+ 2
++1
+ INSERT INTO t3 VALUES(0), (0);
+ SELECT * FROM t3;
+ a
+-1
+ 2
++1
+ INSERT INTO t5 VALUES(0), (0);
+ SELECT * FROM t5;
+ a
+-1
+ 2
++1
+ INSERT INTO t7 VALUES(0), (0);
+ SELECT * FROM t7;
+ a
+-1
+ 2
++1
+ INSERT INTO t9 VALUES(0), (0);
+ SELECT * FROM t9;
+ a
+-1
+ 2
++1
+ # Ensure that all changes before the server is killed are persisted.
+ set global innodb_flush_log_at_trx_commit=1;
+ TRUNCATE TABLE t1;
+@@ -498,63 +498,63 @@
+ INSERT INTO t19 VALUES(0), (0);
+ SELECT * FROM t19;
+ a
+-1
+ 2
++1
+ # restart
+ INSERT INTO t1 VALUES(0), (0);
+ SELECT * FROM t1;
+ a
+-1
+ 2
++1
+ INSERT INTO t3 VALUES(0), (0);
+ SELECT * FROM t3;
+ a
+-1
+ 2
++1
+ INSERT INTO t5 VALUES(0), (0);
+ SELECT * FROM t5;
+ a
+-1
+ 2
++1
+ INSERT INTO t7 VALUES(0), (0);
+ SELECT * FROM t7;
+ a
+-1
+ 2
++1
+ INSERT INTO t19 VALUES(0), (0);
+ SELECT * FROM t19;
+ a
+-1
+-2
+-3
+ 4
++3
++2
++1
+ DELETE FROM t19 WHERE a = 4;
+ RENAME TABLE t19 to t9;
+ INSERT INTO t9 VALUES(0), (0);
+ SELECT * FROM t9;
+ a
+-1
+-2
+-3
+-5
+ 6
++5
++3
++2
++1
+ TRUNCATE TABLE t9;
+ INSERT INTO t9 VALUES(0), (0);
+ SELECT * FROM t9;
+ a
+-1
+ 2
++1
+ # Scenario 8: Test ALTER TABLE operations
+ INSERT INTO t3 VALUES(0), (0), (100), (200), (1000);
+ SELECT * FROM t3;
+ a
+-1
+-2
+-3
+-4
+-100
+-200
+ 1000
++200
++100
++4
++3
++2
++1
+ DELETE FROM t3 WHERE a > 300;
+ SELECT MAX(a) AS `Expect 200` FROM t3;
+ Expect 200
+@@ -566,7 +566,7 @@
+ Table	Create Table
+ t3	CREATE TABLE `t3` (
+   `a` smallint(6) NOT NULL AUTO_INCREMENT,
+-  PRIMARY KEY (`a`)
++  PRIMARY KEY (`a` DESC)
+ ) ENGINE=InnoDB AUTO_INCREMENT=201 DEFAULT CHARSET=latin1
+ INSERT INTO t3 VALUES(0);
+ SELECT MAX(a) AS `Expect 201` FROM t3;
+@@ -579,7 +579,7 @@
+ Table	Create Table
+ t3	CREATE TABLE `t3` (
+   `a` smallint(6) NOT NULL AUTO_INCREMENT,
+-  PRIMARY KEY (`a`)
++  PRIMARY KEY (`a` DESC)
+ ) ENGINE=InnoDB AUTO_INCREMENT=500 DEFAULT CHARSET=latin1
+ INSERT INTO t3 VALUES(0);
+ SELECT MAX(a) AS `Expect 500` FROM t3;
+@@ -591,13 +591,13 @@
+ Table	Create Table
+ t3	CREATE TABLE `t3` (
+   `a` smallint(6) NOT NULL AUTO_INCREMENT,
+-  PRIMARY KEY (`a`)
++  PRIMARY KEY (`a` DESC)
+ ) ENGINE=InnoDB AUTO_INCREMENT=100 DEFAULT CHARSET=latin1
+ INSERT INTO t3 VALUES(0), (0);
+ SELECT * FROM t3;
+ a
+-100
+ 101
++100
+ INSERT INTO t3 VALUES(150), (180);
+ UPDATE t3 SET a = 200 WHERE a = 150;
+ INSERT INTO t3 VALUES(220);
+@@ -607,7 +607,7 @@
+ Table	Create Table
+ t3	CREATE TABLE `t3` (
+   `a` smallint(6) NOT NULL AUTO_INCREMENT,
+-  PRIMARY KEY (`a`)
++  PRIMARY KEY (`a` DESC)
+ ) ENGINE=InnoDB AUTO_INCREMENT=221 DEFAULT CHARSET=latin1
+ INSERT INTO t3 VALUES(0);
+ SELECT MAX(a) AS `Expect 221` FROM t3;
+@@ -619,7 +619,7 @@
+ Table	Create Table
+ t3	CREATE TABLE `t3` (
+   `a` smallint(6) NOT NULL AUTO_INCREMENT,
+-  PRIMARY KEY (`a`)
++  PRIMARY KEY (`a` DESC)
+ ) ENGINE=InnoDB AUTO_INCREMENT=120 DEFAULT CHARSET=latin1
+ # MDEV-6076: Test adding an AUTO_INCREMENT COLUMN
+ CREATE TABLE mdev6076a (b INT) ENGINE=InnoDB;
+@@ -669,18 +669,18 @@
+ INSERT INTO t_inplace SELECT * FROM t3;
+ SELECT * FROM t_inplace;
+ a
+-100
+-101
+-120
+-121
+-122
+-200
+ 210
++200
++122
++121
++120
++101
++100
+ SHOW CREATE TABLE t_inplace;
+ Table	Create Table
+ t_inplace	CREATE TABLE `t_inplace` (
+   `a` smallint(6) NOT NULL AUTO_INCREMENT,
+-  PRIMARY KEY (`a`)
++  PRIMARY KEY (`a` DESC)
+ ) ENGINE=InnoDB AUTO_INCREMENT=211 DEFAULT CHARSET=latin1
+ # This will keep the autoinc counter
+ ALTER TABLE t_inplace AUTO_INCREMENT = 250, ALGORITHM = INPLACE;
+@@ -689,7 +689,7 @@
+ Table	Create Table
+ t_inplace	CREATE TABLE `t_inplace` (
+   `a` smallint(6) NOT NULL AUTO_INCREMENT,
+-  PRIMARY KEY (`a`)
++  PRIMARY KEY (`a` DESC)
+ ) ENGINE=InnoDB AUTO_INCREMENT=250 DEFAULT CHARSET=latin1
+ # This should keep the autoinc counter as well
+ ALTER TABLE t_inplace ADD COLUMN b INT, ALGORITHM = INPLACE;
+@@ -699,16 +699,16 @@
+ t_inplace	CREATE TABLE `t_inplace` (
+   `a` smallint(6) NOT NULL AUTO_INCREMENT,
+   `b` int(11) DEFAULT NULL,
+-  PRIMARY KEY (`a`)
++  PRIMARY KEY (`a` DESC)
+ ) ENGINE=InnoDB AUTO_INCREMENT=250 DEFAULT CHARSET=latin1
+ DELETE FROM t_inplace WHERE a > 150;
+ SELECT * FROM t_inplace;
+ a	b
+-100	NULL
+-101	NULL
+-120	NULL
+-121	NULL
+ 122	NULL
++121	NULL
++120	NULL
++101	NULL
++100	NULL
+ # This should reset the autoinc counter to the one specified
+ # Since it's smaller than current one but bigger than existing
+ # biggest counter in the table
+@@ -719,7 +719,7 @@
+ t_inplace	CREATE TABLE `t_inplace` (
+   `a` smallint(6) NOT NULL AUTO_INCREMENT,
+   `b` int(11) DEFAULT NULL,
+-  PRIMARY KEY (`a`)
++  PRIMARY KEY (`a` DESC)
+ ) ENGINE=InnoDB AUTO_INCREMENT=180 DEFAULT CHARSET=latin1
+ # This should reset the autoinc counter to the next value of
+ # current max counter in the table, since the specified value
+@@ -730,7 +730,7 @@
+ Table	Create Table
+ t_inplace	CREATE TABLE `t_inplace` (
+   `a` smallint(6) NOT NULL AUTO_INCREMENT,
+-  PRIMARY KEY (`a`)
++  PRIMARY KEY (`a` DESC)
+ ) ENGINE=InnoDB AUTO_INCREMENT=123 DEFAULT CHARSET=latin1
+ INSERT INTO t_inplace VALUES(0), (0);
+ SELECT MAX(a) AS `Expect 124` FROM t_inplace;
+@@ -757,18 +757,18 @@
+ INSERT INTO t_copy SELECT * FROM t3;
+ SELECT * FROM t_copy;
+ a
+-100
+-101
+-120
+-121
+-122
+-200
+ 210
++200
++122
++121
++120
++101
++100
+ SHOW CREATE TABLE t_copy;
+ Table	Create Table
+ t_copy	CREATE TABLE `t_copy` (
+   `a` smallint(6) NOT NULL AUTO_INCREMENT,
+-  PRIMARY KEY (`a`)
++  PRIMARY KEY (`a` DESC)
+ ) ENGINE=InnoDB AUTO_INCREMENT=211 DEFAULT CHARSET=latin1
+ # This will keep the autoinc counter
+ ALTER TABLE t_copy AUTO_INCREMENT = 250, ALGORITHM = COPY;
+@@ -777,7 +777,7 @@
+ Table	Create Table
+ t_copy	CREATE TABLE `t_copy` (
+   `a` smallint(6) NOT NULL AUTO_INCREMENT,
+-  PRIMARY KEY (`a`)
++  PRIMARY KEY (`a` DESC)
+ ) ENGINE=InnoDB AUTO_INCREMENT=250 DEFAULT CHARSET=latin1
+ # This should keep the autoinc counter as well
+ ALTER TABLE t_copy ADD COLUMN b INT, ALGORITHM = COPY;
+@@ -787,16 +787,16 @@
+ t_copy	CREATE TABLE `t_copy` (
+   `a` smallint(6) NOT NULL AUTO_INCREMENT,
+   `b` int(11) DEFAULT NULL,
+-  PRIMARY KEY (`a`)
++  PRIMARY KEY (`a` DESC)
+ ) ENGINE=InnoDB AUTO_INCREMENT=250 DEFAULT CHARSET=latin1
+ DELETE FROM t_copy WHERE a > 150;
+ SELECT * FROM t_copy;
+ a	b
+-100	NULL
+-101	NULL
+-120	NULL
+-121	NULL
+ 122	NULL
++121	NULL
++120	NULL
++101	NULL
++100	NULL
+ # This should reset the autoinc counter to the one specified
+ # Since it's smaller than current one but bigger than existing
+ # biggest counter in the table
+@@ -807,7 +807,7 @@
+ t_copy	CREATE TABLE `t_copy` (
+   `a` smallint(6) NOT NULL AUTO_INCREMENT,
+   `b` int(11) DEFAULT NULL,
+-  PRIMARY KEY (`a`)
++  PRIMARY KEY (`a` DESC)
+ ) ENGINE=InnoDB AUTO_INCREMENT=180 DEFAULT CHARSET=latin1
+ # This should reset the autoinc counter to the next value of
+ # current max counter in the table, since the specified value
+@@ -818,7 +818,7 @@
+ Table	Create Table
+ t_copy	CREATE TABLE `t_copy` (
+   `a` smallint(6) NOT NULL AUTO_INCREMENT,
+-  PRIMARY KEY (`a`)
++  PRIMARY KEY (`a` DESC)
+ ) ENGINE=InnoDB AUTO_INCREMENT=123 DEFAULT CHARSET=latin1
+ INSERT INTO t_copy VALUES(0), (0);
+ SELECT MAX(a) AS `Expect 124` FROM t_copy;
 @@ -842,7 +842,7 @@
  126
  DROP TABLE t_copy, it_copy;
@@ -124,7 +692,7 @@
  set SQL_MODE = NO_AUTO_VALUE_ON_ZERO;
  INSERT INTO t30 VALUES(NULL, 1), (200, 2), (0, 3);
  INSERT INTO t30(b) VALUES(4), (5), (6), (7);
-@@ -869,7 +869,7 @@
+@@ -869,20 +869,20 @@
  set global innodb_flush_log_at_trx_commit=1;
  CREATE TABLE t31 (a INT) ENGINE = InnoDB;
  INSERT INTO t31 VALUES(1), (2);
@@ -133,8 +701,17 @@
  INSERT INTO t31 VALUES(3, 0), (4, NULL), (5, NULL);
  INSERT INTO t31 VALUES(6, 0);
  ERROR 23000: Duplicate entry '0' for key 'PRIMARY'
-@@ -882,7 +882,7 @@
+ SELECT * FROM t31;
+ a	b
+-3	0
+-1	1
+-2	2
+-4	3
  5	4
++4	3
++2	2
++1	1
++3	0
  SET SQL_MODE = 0;
  # Scenario 10: Rollback would not rollback the counter
 -CREATE TABLE t32 (a BIGINT AUTO_INCREMENT PRIMARY KEY) ENGINE=InnoDB;
@@ -151,6 +728,26 @@
  INSERT INTO t33 VALUES(1, NULL);
  INSERT INTO t33 VALUES(2, NULL);
  INSERT INTO t33 VALUES(2, NULL);
+@@ -920,13 +920,13 @@
+ INSERT INTO t31(a) VALUES(6), (0);
+ SELECT * FROM t31;
+ a	b
+-3	0
+-1	1
+-2	2
+-4	3
+-5	4
+-6	5
+ 0	6
++6	5
++5	4
++4	3
++2	2
++1	1
++3	0
+ DROP TABLE t31;
+ set SQL_MODE = NO_AUTO_VALUE_ON_ZERO;
+ DELETE FROM t30 WHERE a = 0;
 @@ -965,7 +965,7 @@
  DROP TABLE t33;
  CREATE TABLE t33 (
@@ -160,3 +757,13 @@
  ALTER TABLE t33 DISCARD TABLESPACE;
  restore: t33 .ibd and .cfg files
  ALTER TABLE t33 IMPORT TABLESPACE;
+@@ -975,7 +975,7 @@
+ 4
+ SELECT * FROM t33;
+ a	b
+-10	1
+-2	2
+ 3	4
++2	2
++10	1
+ DROP TABLE t1, t2, t3, t4, t5, t6, t7, t8, t9, t10, t11, t12, t30, t32, t33;

mysql-test/suite/innodb/r/innodb-index.result

@@ -1969,7 +1969,7 @@ Table	Create Table
 t1	CREATE TABLE `t1` (
   `id` int(11) NOT NULL,
   PRIMARY KEY (`id`),
-  UNIQUE KEY `id` (`id`)
+  UNIQUE KEY `id` (`id` DESC)
 ) ENGINE=InnoDB DEFAULT CHARSET=latin1
 DROP TABLE t1;
 #

mysql-test/suite/innodb_fts/r/create.result

@@ -194,9 +194,20 @@ ERROR HY000: Index 'FTS_DOC_ID_INDEX' is of wrong type for an InnoDB FULLTEXT in
 CREATE TABLE t1(a INT PRIMARY KEY, b TEXT, FTS_DOC_ID BIGINT UNSIGNED NOT NULL,
 UNIQUE KEY FTS_DOC_ID_INDEX(FTS_DOC_ID DESC), FULLTEXT(b))
 ENGINE=InnoDB;
-DROP TABLE t1;
+ERROR HY000: Index 'FTS_DOC_ID_INDEX' is of wrong type for an InnoDB FULLTEXT index
 CREATE TABLE t1(a INT PRIMARY KEY, b TEXT, FTS_DOC_ID BIGINT UNSIGNED NOT NULL,
 UNIQUE KEY FTS_DOC_ID_INDEX(FTS_DOC_ID DESC)) ENGINE=InnoDB;
+SHOW CREATE TABLE t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `a` int(11) NOT NULL,
+  `b` text DEFAULT NULL,
+  `FTS_DOC_ID` bigint(20) unsigned NOT NULL,
+  PRIMARY KEY (`a`),
+  UNIQUE KEY `FTS_DOC_ID_INDEX` (`FTS_DOC_ID` DESC)
+) ENGINE=InnoDB DEFAULT CHARSET=latin1
 ALTER TABLE t1 ADD FULLTEXT INDEX(b), ALGORITHM=INPLACE;
+ERROR HY000: Index 'FTS_DOC_ID_INDEX' is of wrong type for an InnoDB FULLTEXT index
 ALTER TABLE t1 ADD FULLTEXT INDEX(b), ALGORITHM=COPY;
+ERROR HY000: Index 'FTS_DOC_ID_INDEX' is of wrong type for an InnoDB FULLTEXT index
 DROP TABLE t1;

mysql-test/suite/innodb_fts/t/create.test

@@ -122,17 +122,16 @@ engine=innodb;
 --echo # MDEV-26938 Support descending indexes internally in InnoDB
 --echo #
 
-# Unfortunately, the HA_REVERSE_SORT flag is not being stored in the .frm file.
+--error ER_INNODB_FT_WRONG_DOCID_INDEX
-#FIXME: --error ER_INNODB_FT_WRONG_DOCID_INDEX
 CREATE TABLE t1(a INT PRIMARY KEY, b TEXT, FTS_DOC_ID BIGINT UNSIGNED NOT NULL,
                 UNIQUE KEY FTS_DOC_ID_INDEX(FTS_DOC_ID DESC), FULLTEXT(b))
 ENGINE=InnoDB;
-DROP TABLE t1;
 
 CREATE TABLE t1(a INT PRIMARY KEY, b TEXT, FTS_DOC_ID BIGINT UNSIGNED NOT NULL,
                 UNIQUE KEY FTS_DOC_ID_INDEX(FTS_DOC_ID DESC)) ENGINE=InnoDB;
-#FIXME: --error ER_INNODB_FT_WRONG_DOCID_INDEX
+SHOW CREATE TABLE t1;
+--error ER_INNODB_FT_WRONG_DOCID_INDEX
 ALTER TABLE t1 ADD FULLTEXT INDEX(b), ALGORITHM=INPLACE;
-#FIXME: --error ER_INNODB_FT_WRONG_DOCID_INDEX
+--error ER_INNODB_FT_WRONG_DOCID_INDEX
 ALTER TABLE t1 ADD FULLTEXT INDEX(b), ALGORITHM=COPY;
 DROP TABLE t1;

mysql-test/suite/innodb_gis/r/geometry.result

@@ -342,7 +342,7 @@ tab	CREATE TABLE `tab` (
   `c7` geometrycollection DEFAULT NULL,
   `c8` geometry DEFAULT NULL,
   UNIQUE KEY `idx2` (`c8`(5)),
-  KEY `idx1` (`c2`(5)) USING BTREE,
+  KEY `idx1` (`c2`(5) DESC) USING BTREE,
   KEY `idx3` (`c3`(5)) USING BTREE
 ) ENGINE=InnoDB DEFAULT CHARSET=latin1
 #check the data after modify
@@ -778,7 +778,7 @@ tab3	CREATE TABLE `tab3` (
   `c7` geometrycollection DEFAULT NULL,
   `c8` geometry DEFAULT NULL,
   UNIQUE KEY `idx2` (`c8`(5)),
-  KEY `idx1` (`c2`(5)) USING BTREE,
+  KEY `idx1` (`c2`(5) DESC) USING BTREE,
   KEY `idx3` (`c3`(5)) USING BTREE
 ) ENGINE=InnoDB DEFAULT CHARSET=latin1 ROW_FORMAT=DYNAMIC KEY_BLOCK_SIZE=16
 #check index with  WKB function

sql/key.cc

@@ -1,5 +1,5 @@
 /* Copyright (c) 2000, 2010, Oracle and/or its affiliates. All rights reserved.
-   Copyright (c) 2018, 2020, MariaDB
+   Copyright (c) 2018, 2021, MariaDB
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -573,6 +573,9 @@ int key_rec_cmp(void *key_p, uchar *first_rec, uchar *second_rec)
     /* loop over every key part */
     do
     {
+      const int GREATER= key_part->key_part_flag & HA_REVERSE_SORT ? -1 : +1;
+      const int LESS= -GREATER;
+
       field= key_part->field;
 
       if (key_part->null_bit)
@@ -593,12 +596,12 @@ int key_rec_cmp(void *key_p, uchar *first_rec, uchar *second_rec)
             ; /* Fall through, no NULL fields */
           else
           {
-            DBUG_RETURN(+1);
+            DBUG_RETURN(GREATER);
           }
         }
         else if (!sec_is_null)
         {
-          DBUG_RETURN(-1);
+          DBUG_RETURN(LESS);
         }
         else
           goto next_loop; /* Both were NULL */
@@ -612,7 +615,7 @@ int key_rec_cmp(void *key_p, uchar *first_rec, uchar *second_rec)
       */
       if ((result= field->cmp_prefix(field->ptr+first_diff, field->ptr+sec_diff,
                                      key_part->length)))
-        DBUG_RETURN(result);
+        DBUG_RETURN(result * GREATER);
 next_loop:
       key_part++;
       key_part_num++;

sql/opt_range.cc

@@ -1,5 +1,5 @@
 /* Copyright (c) 2000, 2015, Oracle and/or its affiliates.
-   Copyright (c) 2008, 2020, MariaDB
+   Copyright (c) 2008, 2021, MariaDB
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -2805,11 +2805,11 @@ int SQL_SELECT::test_quick_select(THD *thd, key_map keys_to_use,
         continue;    // ToDo: ft-keys in non-ft ranges, if possible   SerG
       }
 
-      trace_idx_details.add("usable", true);
       param.key[param.keys]=key_parts;
       key_part_info= key_info->key_part;
       uint cur_key_len= 0;
       Json_writer_array trace_keypart(thd, "key_parts");
+      bool unusable_has_desc_keyparts= false;
       for (uint part= 0 ; part < n_key_parts ; 
            part++, key_parts++, key_part_info++)
       {
@@ -2824,8 +2824,17 @@ int SQL_SELECT::test_quick_select(THD *thd, key_map keys_to_use,
           (key_info->flags & HA_SPATIAL) ? Field::itMBR : Field::itRAW;
         /* Only HA_PART_KEY_SEG is used */
         key_parts->flag=         (uint8) key_part_info->key_part_flag;
+        if (key_part_info->key_part_flag & HA_REVERSE_SORT)
+          unusable_has_desc_keyparts= true;
         trace_keypart.add(key_parts->field->field_name);
       }
+      trace_keypart.end();
+      trace_idx_details.add("usable", !unusable_has_desc_keyparts);
+      if (unusable_has_desc_keyparts) // TODO MDEV-13756
+      {
+        key_parts= param.key[param.keys];
+        continue;
+      }
       param.real_keynr[param.keys++]=idx;
       if (cur_key_len > max_key_len)
         max_key_len= cur_key_len;

sql/opt_sum.cc

@@ -1,5 +1,5 @@
 /* Copyright (c) 2000, 2011, Oracle and/or its affiliates.
-   Copyright (c) 2008, 2017, MariaDB Corporation.
+   Copyright (c) 2008, 2021, MariaDB Corporation.
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -953,6 +953,9 @@ static bool find_key_for_maxmin(bool max_fl, TABLE_REF *ref,
           part->length < part_field->key_length())
         break;
 
+      if (part->key_part_flag & HA_REVERSE_SORT)
+        break; // TODO MDEV-27576
+
       if (field->eq(part->field))
       {
         ref->key= idx;

sql/sql_class.h

@@ -290,9 +290,9 @@ class Key_part_spec :public Sql_alloc {
 public:
   LEX_CSTRING field_name;
   uint length;
-  bool generated;
+  bool generated, asc;
   Key_part_spec(const LEX_CSTRING *name, uint len, bool gen= false)
-    : field_name(*name), length(len), generated(gen)
+    : field_name(*name), length(len), generated(gen), asc(1)
   {}
   bool operator==(const Key_part_spec& other) const;
   /**

sql/sql_show.cc

@@ -2369,6 +2369,8 @@ int show_create_table_ex(THD *thd, TABLE_LIST *table_list,
         packet->append_parenthesized((long) key_part->length /
                                       key_part->field->charset()->mbmaxlen);
       }
+      if (key_part->key_part_flag & HA_REVERSE_SORT)
+        packet->append(STRING_WITH_LEN(" DESC"));
     }
 
     if (key_info->without_overlaps)

sql/sql_table.cc

@@ -2281,7 +2281,7 @@ void promote_first_timestamp_column(List<Create_field> *column_definitions)
 
 static bool key_cmp(const Key_part_spec &a, const Key_part_spec &b)
 {
-  return a.length == b.length &&
+  return a.length == b.length && a.asc == b.asc &&
          !lex_string_cmp(system_charset_info, &a.field_name, &b.field_name);
 }
 
@@ -3328,6 +3328,7 @@ mysql_prepare_create_table(THD *thd, HA_CREATE_INFO *create_info,
       key_part_info->fieldnr= field;
       key_part_info->offset=  (uint16) sql_field->offset;
       key_part_info->key_type=sql_field->pack_flag;
+      key_part_info->key_part_flag= column->asc ? 0 : HA_REVERSE_SORT;
       uint key_part_length= sql_field->type_handler()->
                               calc_key_length(*sql_field);
 
@@ -6335,6 +6336,14 @@ Compare_keys compare_keys_but_name(const KEY *table_key, const KEY *new_key,
       return Compare_keys::NotEqual;
     }
 
+    /*
+      Check the descending flag for index field.
+    */
+    if ((new_part->key_part_flag ^ key_part->key_part_flag) & HA_REVERSE_SORT)
+    {
+      return Compare_keys::NotEqual;
+    }
+
     auto compare= table->file->compare_key_parts(
         *table->field[key_part->fieldnr - 1], new_field, *key_part, *new_part);
     result= merge(result, compare);
@@ -8386,9 +8395,10 @@ mysql_prepare_alter_table(THD *thd, TABLE *table,
 	  key_part_length= 0;			// Use whole field
       }
       key_part_length /= kfield->charset()->mbmaxlen;
-      key_parts.push_back(new (thd->mem_root) Key_part_spec(&cfield->field_name,
+      Key_part_spec *kps= new (thd->mem_root) Key_part_spec(&cfield->field_name,
-                                                            key_part_length, true),
+                                                            key_part_length, true);
-                          thd->mem_root);
+      kps->asc= !(key_part->key_part_flag & HA_REVERSE_SORT);
+      key_parts.push_back(kps, thd->mem_root);
       if (!(cfield->invisible == INVISIBLE_SYSTEM && cfield->vers_sys_field()))
         user_keyparts= true;
     }

sql/sql_yacc.yy

@@ -6803,10 +6803,12 @@ ignorability:
 key_list:
           key_list ',' key_part order_dir
           {
+            $3->asc= $4;
             Lex->last_key->columns.push_back($3, thd->mem_root);
           }
         | key_part order_dir
           {
+            $1->asc= $2;
             Lex->last_key->columns.push_back($1, thd->mem_root);
           }
         ;

sql/unireg.cc

@@ -1,6 +1,6 @@
 /*
    Copyright (c) 2000, 2011, Oracle and/or its affiliates.
-   Copyright (c) 2009, 2020, MariaDB Corporation.
+   Copyright (c) 2009, 2021, MariaDB Corporation.
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -685,6 +685,13 @@ static uint pack_keys(uchar *keybuff, uint key_count, KEY *keyinfo,
     DBUG_PRINT("loop", ("flags: %lu  key_parts: %d  key_part: %p",
                         key->flags, key->user_defined_key_parts,
                         key->key_part));
+
+    /* For SPATIAL, FULLTEXT and HASH indexes (anything other than B-tree),
+       ignore the ASC/DESC attribute of columns. */
+    const uchar ha_reverse_sort=
+      key->algorithm > HA_KEY_ALG_BTREE || key->flags & (HA_FULLTEXT|HA_SPATIAL)
+      ? 0 : HA_REVERSE_SORT;
+
     for (key_part=key->key_part,key_part_end=key_part+key->user_defined_key_parts ;
 	 key_part != key_part_end ;
 	 key_part++)
@@ -697,7 +704,8 @@ static uint pack_keys(uchar *keybuff, uint key_count, KEY *keyinfo,
       int2store(pos,key_part->fieldnr+1+FIELD_NAME_USED);
       offset= (uint) (key_part->offset+data_offset+1);
       int2store(pos+2, offset);
-      pos[4]=0;					// Sort order
+      key_part->key_part_flag &= ha_reverse_sort;
+      pos[4]= (uchar)(key_part->key_part_flag);
       int2store(pos+5,key_part->key_type);
       int2store(pos+7,key_part->length);
       pos+=9;