Table and Query optimization - mysql

Question

Simple web app, hosted on standard shared hosting using PHp and MySql backend.
I have two relatively small tables (few hundred rows in each) that when I query with a join the query can take two to three seconds.
Here's one table: 'students':
CREATE TABLE IF NOT EXISTS `students` (
`_id` mediumint(9) NOT NULL AUTO_INCREMENT,
`firstname` char(30) NOT NULL,
`lastname` char(30) NOT NULL,
`dateOfBirth` date DEFAULT NULL,
`gender` varchar(10) NOT NULL,
`knownasname` varchar(30) NOT NULL,
`school` varchar(30) DEFAULT NULL,
`schoolyear` varchar(30) DEFAULT NULL,
`notes` text,
`foundusvia` varchar(30) DEFAULT NULL,
`dateadded` datetime NOT NULL,
`archived` tinyint(1) DEFAULT NULL,
PRIMARY KEY (`_id`),
UNIQUE KEY `_id` (`_id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 AUTO_INCREMENT=684 ;
Here's the second:
CREATE TABLE IF NOT EXISTS `contacts` (
`_id` mediumint(9) NOT NULL AUTO_INCREMENT,
`student_id` mediumint(9) NOT NULL,
`studentAddressStreet` varchar(50) DEFAULT NULL,
`studentAddressArea` varchar(30) DEFAULT NULL,
`studentAddressTown` varchar(30) DEFAULT NULL,
`studentAddressPostcode` varchar(30) DEFAULT NULL,
`studentPhoneMobile` varchar(30) DEFAULT NULL,
`studentPhoneLand` varchar(30) DEFAULT NULL,
`studentAddressNotes` text,
`studentemail` varchar(50) DEFAULT NULL,
`billingAddressStreet` varchar(50) DEFAULT NULL,
`billingAddressArea` varchar(30) DEFAULT NULL,
`billingAddressTown` varchar(30) DEFAULT NULL,
`billingAddressPostcode` varchar(30) DEFAULT NULL,
`billingPhoneMobile` varchar(30) DEFAULT NULL,
`billingPhoneLand` varchar(30) DEFAULT NULL,
`billingContactName` varchar(30) DEFAULT NULL,
`billingContactRelationship` varchar(30) DEFAULT NULL,
`billingAddressNotes` text,
`billingemail` varchar(50) DEFAULT NULL,
`caregiverAddressStreet` varchar(50) DEFAULT NULL,
`caregiverAddressArea` varchar(30) DEFAULT NULL,
`caregiverAddressTown` varchar(30) DEFAULT NULL,
`caregiverAddressPostcode` varchar(30) DEFAULT NULL,
`caregiverPhoneMobile` varchar(30) DEFAULT NULL,
`caregiverPhoneLand` varchar(30) DEFAULT NULL,
`caregiverContactName` varchar(30) DEFAULT NULL,
`caregiverContactRelationship` varchar(30) DEFAULT NULL,
`caregiverAddressNotes` text,
`caregiveremail` varchar(50) DEFAULT NULL,
PRIMARY KEY (`_id`),
KEY `contacts_index` (`student_id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 AUTO_INCREMENT=290 ;
Here's the query:
Its job is to get all the data from the table "students' and 'contacts' for the student with a given _id.
SELECT *
FROM students, contacts
WHERE students._id = contacts.student_id
AND students._id =99 <=== This value obviously changes
The table contacts has an index on student_id
The table students has an index on firstname and lastname.
What is wrong to make this query take 2 to 3 seconds to run? The tables are small and the query simple. Any help greatly appreciated!!
edit: here's the output of EXPLAIN. Also revised CREATE for contacts table
id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra
===|=============|=========|======|===============|==============|=========|======|=============
1 | SIMPLE | students|const | PRIMARY | PRIMARY | 3 |const | 1 |
1 | SIMPLE | contacts|ref | contacts_index|contacts_index| 3 |const | 1 |

Answer 1

Pro tip: If at all possible avoid SELECT *. It's especially problematic on JOINs.
You'll have an easier time reading your query if you use a standard JOIN, like so. That comma-separated list of tables jumped the shark sometime in the late 1990s.
SELECT students.*,
contacts.*
FROM students
LEFT JOIN contacts ON students._id = contacts.student_id
WHERE students._id =99
Finally, put an index on the student_id column of the contacts table so the join can quickly access that table.