PHP/mysql dynamic dependent dropdown

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PHP

MySQL

Hello,
I need to create a student database to a college. i create it. Now i need to add a form which contains dependent dropdown list in it. That the form need to have 3 dropdown list on is show the dept(department) and next need to show the selected department related years the final one need to show the sections of selected year of department. my database name is department and my table name is students.my table is
Table structure for table `students`
--

CREATE TABLE IF NOT EXISTS `students` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(200) NOT NULL,
`faname` varchar(200) NOT NULL,
`dept` varchar(200) NOT NULL,
`year` int(200) NOT NULL,
`section` varchar(200) NOT NULL,
`contact` varchar(30) NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=MyISAM DEFAULT CHARSET=latin1 AUTO_INCREMENT=46 ;

--
-- Dumping data for table `students`
--

INSERT INTO `students` (`id`, `name`, `faname`, `dept`, `year`, `section`, `contact`) VALUES
(43, 'Vetri Kumar', 'Raja', 'BABL', 4, 'A', '9500671384'),
(38, 'Nandhini', 'Krishnan', 'BCA', 3, 'A', '9965224881'),
(39, 'Sakthi', 'Mahendhran', 'BABL', 3, 'B', '8608769454'),
(44, 'raji', 'raja', 'BABL', 4, 'B', '9874563210'),
(45, 'Nithi', 'devraj', 'BCA', 3, 'A', '9865230140');