Description:
------------
this code has not any problem:
exec('C:/mysql/bin/mysqldump.exe --user=root --password=123456 --host=localhost mydb > D:\myfile.sql');

but this:
exec('mydb > D:\myfile.sql');
is any program executed in this? but it create the file with 0byte
so now you can create any type of files
exec('mydb > D:\myfile.php');
exec('mydb > D:\myfile.exe');
exec('mydb > D:\myfile.txt');

Test script:
---------------
exec('mydb > D:\myfile.php');
exec('mydb > D:\myfile.exe');
exec('mydb > D:\myfile.txt');