I've this during my PHP code, which results MySql errors:

$res = mysql_query($sql) or die(mysql_error());

Will crippling error confirming in php.ini cause these mysql errors to not show too?

No, because die() prints the string and exit. It has nothing related to *error_confirming*. For production atmosphere you need to consider a logger to create such message to some file or somewhere, rather than printing it.