我在亚马逊Linux上做过yum搜索mysql，只有以下内容可用：
php-mysql.x86_64 : A module for PHP applications that use MySQL databases
php-mysqlnd.x86_64 : A module for PHP applications that use MySQL databases
php54-mysql.x86_64 : A module for PHP applications that use MySQL databases
php54-mysqlnd.x86_64 : A module for PHP applications that use MySQL databases
php55-mysqlnd.x86_64 : A module for PHP applications that use MySQL databases
php56-mysqlnd.x86_64 : A module for PHP applications that use MySQL databases
如何安装php55-mysql？我不想要php55-mysqlnd，因为Native Driver会返回Integer而不是String来查询。