MDEV-6683 A parameter and a string literal with the same values are not...

MDEV-6683 A parameter and a string literal with the same values are not recognized as equal by the optimizer

mysql-test/r/ctype_utf8.result

@@ -5977,15 +5977,22 @@ EXECUTE stmt USING @arg;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t1	range	a	a	33	NULL	1	Using index condition
 DEALLOCATE PREPARE stmt;
-ALTER TABLE t1 CONVERT TO CHARACTER SET latin1;
+DROP TABLE t1;
+#
+# MDEV-6683 A parameter and a string literal with the same values are not recognized as equal by the optimizer
+#
+SET NAMES utf8, collation_connection=utf8_swedish_ci;
+CREATE TABLE t1 (a VARCHAR(10) CHARACTER SET latin1, b INT NOT NULL DEFAULT 0, key(a));
+INSERT INTO t1 (a) VALUES ('a'),('b'),('c'),('d'),('¢');
+SET @arg='¢';
 PREPARE stmt FROM "EXPLAIN SELECT * FROM t1 WHERE a BETWEEN _utf8'¢' and ?";
 EXECUTE stmt USING @arg;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t1	range	a	a	13	NULL	1	Using index condition
+1	SIMPLE	t1	ref	a	a	13	const	1	Using index condition
 PREPARE stmt FROM "EXPLAIN SELECT * FROM t1 WHERE a between ? and _utf8'¢'";
 EXECUTE stmt USING @arg;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t1	range	a	a	13	NULL	1	Using index condition
+1	SIMPLE	t1	ref	a	a	13	const	1	Using index condition
 DEALLOCATE PREPARE stmt;
 DROP TABLE t1;
 #

mysql-test/t/ctype_utf8.test

@@ -1693,8 +1693,16 @@ EXECUTE stmt USING @arg;
 PREPARE stmt FROM "EXPLAIN SELECT * FROM t1 WHERE a between ? and _utf8'¢'";
 EXECUTE stmt USING @arg;
 DEALLOCATE PREPARE stmt;
+DROP TABLE t1;
+
+-- echo #
+-- echo # MDEV-6683 A parameter and a string literal with the same values are not recognized as equal by the optimizer
+-- echo #
 
-ALTER TABLE t1 CONVERT TO CHARACTER SET latin1;
+SET NAMES utf8, collation_connection=utf8_swedish_ci;
+CREATE TABLE t1 (a VARCHAR(10) CHARACTER SET latin1, b INT NOT NULL DEFAULT 0, key(a));
+INSERT INTO t1 (a) VALUES ('a'),('b'),('c'),('d'),('¢');
+SET @arg='¢';
 PREPARE stmt FROM "EXPLAIN SELECT * FROM t1 WHERE a BETWEEN _utf8'¢' and ?";
 EXECUTE stmt USING @arg;
 PREPARE stmt FROM "EXPLAIN SELECT * FROM t1 WHERE a between ? and _utf8'¢'";

sql/item.cc

@@ -1288,6 +1288,7 @@ Item *Item_param::safe_charset_converter(CHARSET_INFO *tocs)
         !cnvitem->check_well_formed_result(&cnvitem->str_value, true))
       return NULL;
     cnvitem->str_value.mark_as_const();
+    cnvitem->collation.set(tocs);
     cnvitem->max_length= cnvitem->str_value.numchars() * tocs->mbmaxlen;
     return cnvitem;
   }