MDEV-6105: Emoji unicode character string search query makes mariadb performance down

- When range optimizer cannot the lookup value into [VAR]CHAR(n) column,
  it should produce:
  = "Impossible range" for equality
  = "no range" for non-equalities.

1 files changed, 54 insertions, 0 deletions

diff --git a/mysql-test/r/range.result b/mysql-test/r/range.result
index d41bfaa2c67..21acfee897e 100644
--- a/mysql-test/r/range.result
+++ b/mysql-test/r/range.result
@@ -2046,3 +2046,57 @@ f1	f2	f3	f4
 10	0	0	0
 DROP TABLE t1;
 DROP VIEW v3;
+#
+# MDEV-6105: Emoji unicode character string search query makes mariadb performance down
+#
+SET NAMES utf8;
+DROP TABLE IF EXISTS t1;
+Warnings:
+Note	1051	Unknown table 't1'
+CREATE TABLE t1(
+id int AUTO_INCREMENT,
+fd varchar(20),
+primary key(id),
+index ix_fd(fd)
+)engine=innodb default charset=UTF8;
+INSERT INTO t1(id, fd) VALUES (null, ''),(null, 'matt'),(null, 'pitt'),(null, 'lee'),(null, 'kim');
+INSERT INTO t1 (fd) SELECT fd FROM t1;
+INSERT INTO t1 (fd) SELECT fd FROM t1;
+INSERT INTO t1 (fd) SELECT fd FROM t1;
+INSERT INTO t1 (fd) SELECT fd FROM t1;
+INSERT INTO t1 (fd) SELECT fd FROM t1;
+INSERT INTO t1 (fd) SELECT fd FROM t1;
+INSERT INTO t1 (fd) SELECT fd FROM t1;
+INSERT INTO t1 (fd) SELECT fd FROM t1;
+INSERT INTO t1 (fd) SELECT fd FROM t1;
+INSERT INTO t1 (fd) SELECT fd FROM t1;
+INSERT INTO t1 (fd) SELECT fd FROM t1;
+INSERT INTO t1 (fd) SELECT fd FROM t1;
+INSERT INTO t1 (fd) SELECT fd FROM t1;
+# The following should show "Impossible WHERE" :
+explain
+SELECT * FROM t1 WHERE fd='😁';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE noticed after reading const tables
+Warnings:
+Warning	1366	Incorrect string value: '\xF0\x9F\x98\x81' for column 'fd' at row 1
+SELECT * FROM t1 WHERE fd='😁';
+id	fd
+Warnings:
+Warning	1366	Incorrect string value: '\xF0\x9F\x98\x81' for column 'fd' at row 1
+# The following must not use range access:
+explain select count(*) from t1 where fd <'😁';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	index	ix_fd	ix_fd	63	NULL	41410	Using where; Using index
+Warnings:
+Warning	1366	Incorrect string value: '\xF0\x9F\x98\x81' for column 'fd' at row 1
+select count(*) from t1 where fd <'😁';
+count(*)
+40960
+Warnings:
+Warning	1366	Incorrect string value: '\xF0\x9F\x98\x81' for column 'fd' at row 1
+select count(*) from t1 ignore index (ix_fd) where fd <'😁';
+count(*)
+40960
+drop table t1;
+set names default;