MDEV-23852 alter table rename column to uppercase doesn't work

Case-sensitive compare to detect column name case change in inplace
alter rename.

4 files changed, 52 insertions, 18 deletions

diff --git a/mysql-test/main/alter_table.result b/mysql-test/main/alter_table.result
index 197e52b35ca..d717820d621 100644
--- a/mysql-test/main/alter_table.result
+++ b/mysql-test/main/alter_table.result
@@ -3322,5 +3322,28 @@ Note	1176	Key 'x' doesn't exist in table 't1'
 unlock tables;
 drop table t1;
 #
+# MDEV-23852 alter table rename column to uppercase doesn't work
+#
+create table t1 (abc int);
+alter table t1 rename column abc to Abc, algorithm=copy;
+show create table t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `Abc` int(11) DEFAULT NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1
+alter table t1 rename column abc to ABc, algorithm=inplace;
+show create table t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `ABc` int(11) DEFAULT NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1
+alter table t1 rename column abc to ABC;
+show create table t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `ABC` int(11) DEFAULT NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1
+drop table t1;
+#
 # End of 10.5 tests
 #
diff --git a/mysql-test/main/alter_table.test b/mysql-test/main/alter_table.test
index 6fe61a3222a..f5d3fdea907 100644
--- a/mysql-test/main/alter_table.test
+++ b/mysql-test/main/alter_table.test
@@ -2530,5 +2530,17 @@ unlock tables;
 drop table t1;
 
 --echo #
+--echo # MDEV-23852 alter table rename column to uppercase doesn't work
+--echo #
+create table t1 (abc int);
+alter table t1 rename column abc to Abc, algorithm=copy;
+show create table t1;
+alter table t1 rename column abc to ABc, algorithm=inplace;
+show create table t1;
+alter table t1 rename column abc to ABC;
+show create table t1;
+drop table t1;
+
+--echo #
 --echo # End of 10.5 tests
 --echo #
diff --git a/mysql-test/suite/innodb/r/innodb-alter.result b/mysql-test/suite/innodb/r/innodb-alter.result
index 4bd1a09dd73..59abdb01d82 100644
--- a/mysql-test/suite/innodb/r/innodb-alter.result
+++ b/mysql-test/suite/innodb/r/innodb-alter.result
@@ -738,7 +738,7 @@ Table	Create Table
 t2	CREATE TABLE `t2` (
   `C2` int(11) DEFAULT NULL,
   KEY `c2` (`C2`),
-  CONSTRAINT `t2_ibfk_1` FOREIGN KEY (`c2`) REFERENCES `t1` (`c1`)
+  CONSTRAINT `t2_ibfk_1` FOREIGN KEY (`C2`) REFERENCES `t1` (`C1`)
 ) ENGINE=InnoDB DEFAULT CHARSET=latin1
 ALTER TABLE t1 CHANGE COLUMN C1 c5 INT;
 ALTER TABLE t2 CHANGE COLUMN C2 c6 INT;
@@ -785,7 +785,7 @@ SELECT C.NAME FROM INFORMATION_SCHEMA.INNODB_SYS_COLUMNS C INNER JOIN
 INFORMATION_SCHEMA.INNODB_SYS_TABLES T ON C.TABLE_ID=T.TABLE_ID
 WHERE T.NAME='test/t1';
 NAME
-a
+A
 b
 DROP TABLE t1;
 # different FOREIGN KEY cases
@@ -842,27 +842,27 @@ t2	CREATE TABLE `t2` (
   KEY `bb` (`BB`),
   KEY `CC` (`CC`),
   KEY `DD` (`DD`),
-  CONSTRAINT `t2_ibfk_1` FOREIGN KEY (`aa`) REFERENCES `t1` (`a`),
-  CONSTRAINT `t2_ibfk_2` FOREIGN KEY (`bb`) REFERENCES `t1` (`b`),
-  CONSTRAINT `t2_ibfk_3` FOREIGN KEY (`cc`) REFERENCES `t1` (`c`),
-  CONSTRAINT `t2_ibfk_4` FOREIGN KEY (`dd`) REFERENCES `t1` (`d`)
+  CONSTRAINT `t2_ibfk_1` FOREIGN KEY (`AA`) REFERENCES `t1` (`A`),
+  CONSTRAINT `t2_ibfk_2` FOREIGN KEY (`BB`) REFERENCES `t1` (`B`),
+  CONSTRAINT `t2_ibfk_3` FOREIGN KEY (`CC`) REFERENCES `t1` (`C`),
+  CONSTRAINT `t2_ibfk_4` FOREIGN KEY (`DD`) REFERENCES `t1` (`D`)
 ) ENGINE=InnoDB DEFAULT CHARSET=latin1
 DELETE FROM t1 WHERE a=1;
-ERROR 23000: Cannot delete or update a parent row: a foreign key constraint fails (`test`.`t2`, CONSTRAINT `t2_ibfk_1` FOREIGN KEY (`aa`) REFERENCES `t1` (`a`))
+ERROR 23000: Cannot delete or update a parent row: a foreign key constraint fails (`test`.`t2`, CONSTRAINT `t2_ibfk_1` FOREIGN KEY (`AA`) REFERENCES `t1` (`A`))
 DELETE FROM t1 WHERE A=1;
-ERROR 23000: Cannot delete or update a parent row: a foreign key constraint fails (`test`.`t2`, CONSTRAINT `t2_ibfk_1` FOREIGN KEY (`aa`) REFERENCES `t1` (`a`))
+ERROR 23000: Cannot delete or update a parent row: a foreign key constraint fails (`test`.`t2`, CONSTRAINT `t2_ibfk_1` FOREIGN KEY (`AA`) REFERENCES `t1` (`A`))
 DELETE FROM t1 WHERE b=1;
-ERROR 23000: Cannot delete or update a parent row: a foreign key constraint fails (`test`.`t2`, CONSTRAINT `t2_ibfk_1` FOREIGN KEY (`aa`) REFERENCES `t1` (`a`))
+ERROR 23000: Cannot delete or update a parent row: a foreign key constraint fails (`test`.`t2`, CONSTRAINT `t2_ibfk_1` FOREIGN KEY (`AA`) REFERENCES `t1` (`A`))
 DELETE FROM t1 WHERE B=1;
-ERROR 23000: Cannot delete or update a parent row: a foreign key constraint fails (`test`.`t2`, CONSTRAINT `t2_ibfk_1` FOREIGN KEY (`aa`) REFERENCES `t1` (`a`))
+ERROR 23000: Cannot delete or update a parent row: a foreign key constraint fails (`test`.`t2`, CONSTRAINT `t2_ibfk_1` FOREIGN KEY (`AA`) REFERENCES `t1` (`A`))
 DELETE FROM t1 WHERE c=1;
-ERROR 23000: Cannot delete or update a parent row: a foreign key constraint fails (`test`.`t2`, CONSTRAINT `t2_ibfk_1` FOREIGN KEY (`aa`) REFERENCES `t1` (`a`))
+ERROR 23000: Cannot delete or update a parent row: a foreign key constraint fails (`test`.`t2`, CONSTRAINT `t2_ibfk_1` FOREIGN KEY (`AA`) REFERENCES `t1` (`A`))
 DELETE FROM t1 WHERE C=1;
-ERROR 23000: Cannot delete or update a parent row: a foreign key constraint fails (`test`.`t2`, CONSTRAINT `t2_ibfk_1` FOREIGN KEY (`aa`) REFERENCES `t1` (`a`))
+ERROR 23000: Cannot delete or update a parent row: a foreign key constraint fails (`test`.`t2`, CONSTRAINT `t2_ibfk_1` FOREIGN KEY (`AA`) REFERENCES `t1` (`A`))
 DELETE FROM t1 WHERE d=1;
-ERROR 23000: Cannot delete or update a parent row: a foreign key constraint fails (`test`.`t2`, CONSTRAINT `t2_ibfk_1` FOREIGN KEY (`aa`) REFERENCES `t1` (`a`))
+ERROR 23000: Cannot delete or update a parent row: a foreign key constraint fails (`test`.`t2`, CONSTRAINT `t2_ibfk_1` FOREIGN KEY (`AA`) REFERENCES `t1` (`A`))
 DELETE FROM t1 WHERE D=1;
-ERROR 23000: Cannot delete or update a parent row: a foreign key constraint fails (`test`.`t2`, CONSTRAINT `t2_ibfk_1` FOREIGN KEY (`aa`) REFERENCES `t1` (`a`))
+ERROR 23000: Cannot delete or update a parent row: a foreign key constraint fails (`test`.`t2`, CONSTRAINT `t2_ibfk_1` FOREIGN KEY (`AA`) REFERENCES `t1` (`A`))
 DROP TABLE t2, t1;
 # virtual columns case too
 CREATE TABLE t1 (a INT, b INT GENERATED ALWAYS AS (a) VIRTUAL) ENGINE = InnoDB;
@@ -877,7 +877,7 @@ SELECT C.NAME FROM INFORMATION_SCHEMA.INNODB_SYS_COLUMNS C INNER JOIN
 INFORMATION_SCHEMA.INNODB_SYS_TABLES T ON C.TABLE_ID=T.TABLE_ID
 WHERE T.NAME='test/t1';
 NAME
-a
+A
 b
 DROP TABLE t1;
 # and an MDEV-18041 regression related to indexes prefixes
diff --git a/sql/sql_table.cc b/sql/sql_table.cc
index 345edf4d75c..31f165ef98a 100644
--- a/sql/sql_table.cc
+++ b/sql/sql_table.cc
@@ -7171,9 +7171,8 @@ static bool fill_alter_inplace_info(THD *thd, TABLE *table, bool varchar,
           ha_alter_info->handler_flags|= ALTER_STORED_COLUMN_TYPE;
       }
 
-      /* Check if field was renamed */
-      if (lex_string_cmp(system_charset_info, &field->field_name,
-                         &new_field->field_name))
+      /* Check if field was renamed (case-sensitive for detecting case change) */
+      if (cmp(&field->field_name, &new_field->field_name))
       {
         field->flags|= FIELD_IS_RENAMED;
         ha_alter_info->handler_flags|= ALTER_COLUMN_NAME;