MDEV-9251: Fix MySQL Bug#20755615: InnoDB compares column names case sensitively,

while according to Storage Engine API column names should be compared
case insensitively. This can cause FRM and InnoDB data dictionary to
go out of sync.

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

+CREATE TABLE t1 (D INT) ENGINE=innodb;
+INSERT INTO t1 VALUES (10);
+ALTER TABLE t1 MODIFY COLUMN d INT;
+ALTER TABLE t1 ADD INDEX my_d (d);
+SHOW CREATE TABLE t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `d` int(11) DEFAULT NULL,
+  KEY `my_d` (`d`)
+) ENGINE=InnoDB DEFAULT CHARSET=latin1
+INSERT INTO t1 VALUES (1),(2),(3),(4),(5),(6),(7),(8),(9);
+INSERT INTO t1 SELECT * FROM t1;
+INSERT INTO t1 SELECT * FROM t1;
+INSERT INTO t1 SELECT * FROM t1;
+INSERT INTO t1 SELECT * FROM t1;
+INSERT INTO t1 SELECT * FROM t1;
+INSERT INTO t1 SELECT * FROM t1;
+INSERT INTO t1 SELECT * FROM t1;
+EXPLAIN SELECT d FROM t1 WHERE d = 5;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ref	my_d	my_d	5	const	128	Using index
+EXPLAIN SELECT D FROM t1 WHERE D = 5;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ref	my_d	my_d	5	const	128	Using index
+ALTER TABLE t1 DROP INDEX my_d;
+ALTER TABLE t1 MODIFY COLUMN D INT;
+ALTER TABLE t1 ADD INDEX my_d (D);
+EXPLAIN SELECT d FROM t1 WHERE d = 5;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ref	my_d	my_d	5	const	128	Using index
+EXPLAIN SELECT D FROM t1 WHERE D = 5;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ref	my_d	my_d	5	const	128	Using index
+SHOW CREATE TABLE t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `D` int(11) DEFAULT NULL,
+  KEY `my_d` (`D`)
+) ENGINE=InnoDB DEFAULT CHARSET=latin1
+DROP TABLE t1;

mysql-test/suite/innodb/t/innodb-dict.test

+--source include/have_innodb.inc
+
+#
+# Fix MySQL Bug#20755615: InnoDB compares column names case sensitively,
+# while according to Storage Engine API column names should be compared
+# case insensitively. This can cause FRM and InnoDB data dictionary to
+# go out of sync:
+#
+
+CREATE TABLE t1 (D INT) ENGINE=innodb;
+INSERT INTO t1 VALUES (10);
+ALTER TABLE t1 MODIFY COLUMN d INT;
+ALTER TABLE t1 ADD INDEX my_d (d);
+SHOW CREATE TABLE t1;
+INSERT INTO t1 VALUES (1),(2),(3),(4),(5),(6),(7),(8),(9);
+INSERT INTO t1 SELECT * FROM t1;
+INSERT INTO t1 SELECT * FROM t1;
+INSERT INTO t1 SELECT * FROM t1;
+INSERT INTO t1 SELECT * FROM t1;
+INSERT INTO t1 SELECT * FROM t1;
+INSERT INTO t1 SELECT * FROM t1;
+INSERT INTO t1 SELECT * FROM t1;
+EXPLAIN SELECT d FROM t1 WHERE d = 5;
+EXPLAIN SELECT D FROM t1 WHERE D = 5;
+ALTER TABLE t1 DROP INDEX my_d;
+ALTER TABLE t1 MODIFY COLUMN D INT;
+ALTER TABLE t1 ADD INDEX my_d (D);
+EXPLAIN SELECT d FROM t1 WHERE d = 5;
+EXPLAIN SELECT D FROM t1 WHERE D = 5;
+SHOW CREATE TABLE t1;
+DROP TABLE t1;

storage/innobase/dict/dict0dict.c

@@ -2010,7 +2010,7 @@ dict_index_find_cols(
 		dict_field_t*	field = dict_index_get_nth_field(index, i);
 
 		for (j = 0; j < table->n_cols; j++) {
-			if (!strcmp(dict_table_get_col_name(table, j),
+			if (!innobase_strcasecmp(dict_table_get_col_name(table, j),
 				    field->name)) {
 				field->col = dict_table_get_nth_col(table, j);
 

storage/xtradb/dict/dict0dict.c

@@ -2142,7 +2142,7 @@ dict_index_find_cols(
 		dict_field_t*	field = dict_index_get_nth_field(index, i);
 
 		for (j = 0; j < table->n_cols; j++) {
-			if (!strcmp(dict_table_get_col_name(table, j),
+			if (!innobase_strcasecmp(dict_table_get_col_name(table, j),
 				    field->name)) {
 				field->col = dict_table_get_nth_col(table, j);