PHP & MySQL Update Database Problems - php

Question

I'm trying to change my rating system which only used one table before but now I'm changing it to use multiple tables and I really dont no how to
update or insert a new rating into the database and was wondering how to do this using my MySQL tables structure?
Also how do I do this by adapting the new code to my current PHP code which I want to change which is listed below.
First let me explain what my tables do they hold the information when students rate there own teachers I listed what the tables will hold in the
examples below to give you a better understanding of what I'm trying to do. Students are only allowed to rate there teachers once.
I provided the two MySQL tables that should be updated which are listed below.
My MySQL tables
CREATE TABLE teachers_grades (
id INT UNSIGNED NOT NULL AUTO_INCREMENT,
grade_id INT UNSIGNED NOT NULL,
teachers_id INT UNSIGNED NOT NULL,
student_id INT UNSIGNED NOT NULL,
date_created DATETIME NOT NULL,
PRIMARY KEY (id)
);
CREATE TABLE grades (
id INT UNSIGNED NOT NULL AUTO_INCREMENT,
letter_grade VARCHAR(2) NOT NULL,
grade_points FLOAT UNSIGNED NOT NULL DEFAULT 0,
PRIMARY KEY (id)
);
What the database will hold.
teachers_grades
id grade_id teachers_id student_id date_created
1 3 2 32 2010-01-23 04:24:51
2 1 32 3 2010-01-23 12:13:58
3 2 32 103 2010-01-23 12:24:45
grades
id letter_grade points
1 A+ 10
2 D 3
3 B 5
Here is the old PHP code.
// function to insert rating
function rate(){
$text = strip_tags($_GET['rating']);
$update = "update vote set counter = counter + 1, value = value + ".$_GET['rating']."";
$result = mysql_query($update);
if(mysql_affected_rows() == 0){
$insert = "insert into vote (counter,value) values ('1','".$_GET['rating']."')";
$result = mysql_query($insert);
}
}
Old table.
CREATE TABLE vote (
`counter` int(8) NOT NULL default '0',
`value` int(8) NOT NULL default '0'
);

Answer 1

first , do mysql_escape_string to the parametrs when inserting like :
mysql_real_escape_string($_GET['rating']);
second
you need to get all parameters (from GET or POST) and insert it to the db ,
the teacher_id ....
now i only see the rating.

Answer 2

Your old table was bit confusing as it seems like it only rates 1 teacher or teachers as a whole.
Now it seems like your new design process requires you to:
- store rating and averages of teachers
- track historical ratings from students
rating table should look something like
Table: rating
rating_id student_id teacher_id grade_id date_created
1 101 21 1 2010-01-23 04:24:51
2 102 21 1 2010-01-23 04:26:51
3 102 22 2 2010-01-23 04:28:51
4 103 24 1 2010-01-23 04:44:51
Your code usage:
$rating_value = $_GET['rating']; // Remember to sanitize your inputs
$student_id = $_GET['student_id'];
$teacher_id = $_GET['teacher_id'];
rate_a_teacher($teacher_id, $student_id, $rating_value);
Your method:
function rate_a_teacher($teacher_id, $student_id, $rating_value)
{
// Find the corrosponding to specified rating value
$grade_id = find_grade_id($rating_value); //TODO
$sql = "
INSERT INTO rating
('student_id', 'teacher_id', 'grade_id', 'date_created')
VALUE
($student_id, $teacher_id, $grade_id, NOW);
";
mysql_query($sql);
}
I skipped implementation for find_grade_id() for you to fill it in yourself.
The purpose of splitting your calcualted values to individual records is so that you can start do interesting reports,
like such:
Find average rating value of each teacher for the past 3 months:
SELECT teacher_id, (SUM(points)/COUNT(rating_id)) AS average_score
FROM rating
LEFT JOIN grades ON grades.id = rating.grade_id
WHERE date_created > SUBDATE(NOW(), INTERVAL 3 MONTH)
GROUP BY teacher_id