MDEV-25748 DROP DATABASE drops unrelated FOREIGN KEY constraints

innodb_drop_database(): Apply binary comparison.
(SYS_FOREIGN.ID unfortunately uses latin1_swedish_ci collation.)

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

@@ -3,12 +3,17 @@
 # COMMIT_INPLACE_ALTER_TABLE
 #
 call mtr.add_suppression("InnoDB: Failed to load table");
+CREATE DATABASE Bug;
+CREATE TABLE Bug.parent(a SERIAL) ENGINE=INNODB;
+CREATE TABLE Bug.child(a SERIAL, FOREIGN KEY f(a) REFERENCES Bug.parent(a))
+ENGINE=INNODB;
 create database bug;
 use bug;
 create table parent(a serial) engine=innodb;
 create table child(a serial, foreign key fk (a) references parent(a))engine=innodb;
 insert into parent values(1);
 insert into child values(1);
+drop database Bug;
 connect  con1,localhost,root,,bug;
 SET DEBUG_SYNC='innodb_rename_table_ready SIGNAL s1 WAIT_FOR s2 EXECUTE 2';
 ALTER TABLE child ROW_FORMAT=DYNAMIC, ALGORITHM=COPY;

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

@@ -2,6 +2,7 @@
 --source include/have_debug_sync.inc
 # The embedded server does not support restarting.
 --source include/not_embedded.inc
+--source include/have_case_sensitive_file_system.inc
 
 --echo #
 --echo # Bug #20476395 DICT_LOAD_FOREIGNS() FAILED IN
@@ -10,6 +11,11 @@
 
 call mtr.add_suppression("InnoDB: Failed to load table");
 
+CREATE DATABASE Bug;
+CREATE TABLE Bug.parent(a SERIAL) ENGINE=INNODB;
+CREATE TABLE Bug.child(a SERIAL, FOREIGN KEY f(a) REFERENCES Bug.parent(a))
+ENGINE=INNODB;
+
 create database bug;
 use bug;
 
@@ -18,6 +24,7 @@ create table child(a serial, foreign key fk (a) references parent(a))engine=inno
 
 insert into parent values(1);
 insert into child values(1);
+drop database Bug;
 
 connect (con1,localhost,root,,bug);
 SET DEBUG_SYNC='innodb_rename_table_ready SIGNAL s1 WAIT_FOR s2 EXECUTE 2';

storage/innobase/handler/ha_innodb.cc

@@ -1424,8 +1424,9 @@ static void innodb_drop_database(handlerton*, char *path)
     "WHILE 1 = 1 LOOP\n"
     "  FETCH fkf INTO fk;\n"
     "  IF (SQL % NOTFOUND) THEN EXIT; END IF;\n"
-    "  IF SUBSTR(fk, 0, LENGTH(:db)) <> :db THEN EXIT; END IF;\n"
-    "  DELETE FROM SYS_FOREIGN_COLS WHERE ID=fk;\n"
+    "  IF TO_BINARY(SUBSTR(fk, 0, LENGTH(:db)))<>TO_BINARY(:db)"
+    " THEN EXIT; END IF;\n"
+    "  DELETE FROM SYS_FOREIGN_COLS WHERE TO_BINARY(ID)=TO_BINARY(fk);\n"
     "  DELETE FROM SYS_FOREIGN WHERE CURRENT OF fkf;\n"
     "END LOOP;\n"
     "CLOSE fkf;\n"