MyISAM index_condition_pushdown handles trailing whitespace comparisons wrong

DROP TABLE IF EXISTS t1;

CREATE TABLE `t1` (

  `id` int(11) NOT NULL AUTO_INCREMENT,

  `v1` varchar(3),

  `v2` varchar(3),

  `v3` int,

  PRIMARY KEY (`id`),

  KEY `idx` (`v1`,`v2`)

) ENGINE=MyISAM;

-- fill table with 1024 rows for a start

INSERT INTO t1 SELECT NULL, 'abc', 'xyz' , 0;

INSERT INTO t1 SELECT NULL, 'abc', 'xyz' , 0 FROM t1;

INSERT INTO t1 SELECT NULL, 'abc', 'xyz' , 0 FROM t1;

INSERT INTO t1 SELECT NULL, 'abc', 'xyz' , 0 FROM t1;

INSERT INTO t1 SELECT NULL, 'abc', 'xyz' , 0 FROM t1;

INSERT INTO t1 SELECT NULL, 'abc', 'xyz' , 0 FROM t1;

INSERT INTO t1 SELECT NULL, 'abc', 'xyz' , 0 FROM t1;

INSERT INTO t1 SELECT NULL, 'abc', 'xyz' , 0 FROM t1;

INSERT INTO t1 SELECT NULL, 'abc', 'xyz' , 0 FROM t1;

INSERT INTO t1 SELECT NULL, 'abc', 'xyz' , 0 FROM t1;

INSERT INTO t1 SELECT NULL, 'abc', 'xyz' , 0 FROM t1;

-- now add 1024 rows each using different patterns

INSERT INTO t1 SELECT NULL, 'abc', ''    , 0 FROM t1 LIMIT 1024;

INSERT INTO t1 SELECT NULL, ''   , 'xyz' , 0 FROM t1 LIMIT 1024;

INSERT INTO t1 SELECT NULL, ''   , ''    , 0 FROM t1 LIMIT 1024;

-- reading directly from the index returns 1024, as expected

SELECT COUNT(*) FROM t1 WHERE v1 = ' ' AND v2 <> ' '; 

-- but when adding the extra colum it switches to index condition pushdown

-- and returns zero instead of 1024

SELECT COUNT(*) FROM t1 WHERE v1 = ' ' AND v2 <> ' ' AND v3 = 0; 

-- forcing the index to be ignored: 1024 rows reported correctly

SELECT COUNT(*) FROM t1 IGNORE INDEX(idx) WHERE v3=0 AND v1 = ' ' AND v2 <> ' ';

-- switching off index_condition_pushdown results in 1024 rows

SET optimizer_switch='index_condition_pushdown=off';

SELECT COUNT(*) FROM t1 WHERE v3=0 AND v1 = ' ' AND v2 <> ' '; 

-- the problem is also specific to MyISAM only

-- InnoDB returns 1024 just fine, even though index condition 

-- pushdown is used

SET optimizer_switch='index_condition_pushdown=on';

ALTER TABLE t1 ENGINE=InnoDB;

SELECT COUNT(*) FROM t1 WHERE v3=0 AND v1 = ' ' AND v2 <> ' '; 

-- Aria handles this correctly, too

ALTER TABLE t1 ENGINE=Aria;

SELECT COUNT(*) FROM t1 WHERE v3=0 AND v1 = ' ' AND v2 <> ' '; 

COUNT(*)

1024

COUNT(*)

1024

COUNT(*)

1024

COUNT(*)

1024

COUNT(*)

1024

COUNT(*)

1024

COUNT(*)

1024

COUNT(*)

0

COUNT(*)

1024

COUNT(*)

1024

COUNT(*)

1024

COUNT(*)

1024