MDEV-28802 DROP DATABASE in InnoDB still is case-insensitive

innodb_drop_database(): Use explicit TO_BINARY casts on
SYS_TABLES.NAME, which for historical reasons uses the wrong collation
latin1_swedish_ci instead of BINARY.

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

@@ -0,0 +1,16 @@
+#
+# MDEV-28802 DROP DATABASE in InnoDB still is case-insensitive
+#
+SET @save_fpt=@@GLOBAL.innodb_file_per_table;
+SET GLOBAL innodb_file_per_table=0;
+CREATE DATABASE Db;
+CREATE TABLE Db.t1 (c1 INT KEY) ENGINE=InnoDB;
+CREATE DATABASE DB;
+DROP DATABASE DB;
+SELECT NAME FROM INFORMATION_SCHEMA.INNODB_SYS_TABLES WHERE NAME LIKE 'D%';
+NAME
+Db/t1
+DROP DATABASE Db;
+SELECT * FROM INFORMATION_SCHEMA.INNODB_SYS_TABLES WHERE NAME LIKE 'D%';
+TABLE_ID	NAME	FLAG	N_COLS	SPACE	ROW_FORMAT	ZIP_PAGE_SIZE	SPACE_TYPE
+SET GLOBAL innodb_file_per_table=@save_fpt;

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

@@ -0,0 +1,17 @@
+--source include/have_innodb.inc
+--source include/have_case_sensitive_file_system.inc
+
+--echo #
+--echo # MDEV-28802 DROP DATABASE in InnoDB still is case-insensitive
+--echo #
+
+SET @save_fpt=@@GLOBAL.innodb_file_per_table;
+SET GLOBAL innodb_file_per_table=0;
+CREATE DATABASE Db;
+CREATE TABLE Db.t1 (c1 INT KEY) ENGINE=InnoDB;
+CREATE DATABASE DB;
+DROP DATABASE DB;
+SELECT NAME FROM INFORMATION_SCHEMA.INNODB_SYS_TABLES WHERE NAME LIKE 'D%';
+DROP DATABASE Db;
+SELECT * FROM INFORMATION_SCHEMA.INNODB_SYS_TABLES WHERE NAME LIKE 'D%';
+SET GLOBAL innodb_file_per_table=@save_fpt;

storage/innobase/handler/ha_innodb.cc

@@ -1476,7 +1476,8 @@ static void innodb_drop_database(handlerton*, char *path)
     "WHILE 1 = 1 LOOP\n"
     "  FETCH tab INTO tid,name;\n"
     "  IF (SQL % NOTFOUND) THEN EXIT; END IF;\n"
-    "  IF SUBSTR(name, 0, LENGTH(:db)) <> :db THEN EXIT; END IF;\n"
+    "  IF TO_BINARY(SUBSTR(name, 0, LENGTH(:db))) <> TO_BINARY(:db)"
+    " THEN EXIT; END IF;\n"
     "  DELETE FROM SYS_COLUMNS WHERE TABLE_ID=tid;\n"
     "  DELETE FROM SYS_TABLES WHERE ID=tid;\n"
     "  OPEN idx;\n"