PHP/MySQL Insert distinct array values - php

Question

I am inserting values into a MySQL table using the code below, and I need to prevent users from inserting the same priority value for each studentname more than once. What is the best way to do this please?
This is the table:
id studentname title academicdiscipline priority
012345678 TEST, NAME Test title 1 Civil 1
012345678 TEST, NAME Test title 2 Civil 2
012345678 TEST, NAME Test title 3 Civil 3
012345678 TEST, NAME Test title 4 Civil 4
012345678 TEST, NAME Test title 5 Civil 5
Code:
if(isset($_POST['submit']) && !empty($_POST['submit'])) {
$ids = $_POST['id'];
$names = $_POST['studentname'];
$titles = $_POST['title'];
$disciplines = $_POST['academicdiscipline'];
$priorities = $_POST['priority'];
foreach($priorities as $key => $priority) {
if ($priority > 0) {
$query = "INSERT INTO flux_project_selection (id, studentname, title, academicdiscipline, priority)
VALUES ( " . mysql_real_escape_string($ids[$key]) . ",
'" . mysql_real_escape_string($names[$key]) . "',
'" . mysql_real_escape_string($titles[$key]) . "',
'" . mysql_real_escape_string($disciplines[$key]) . "',
" . mysql_real_escape_string($priority) . " )";
$retval = mysql_query($query) or die(mysql_error());
}
}
echo "<p> Added.</p><br />";
}

Answer 1

Create index for unique record, using combination of fields
ALTER TABLE table_name ADD UNIQUE INDEX index_name (field1, field2);
it will allow you to add first record but on duplicate entry show Duplicate entry ... for unique index. You can either use try and catch to display error message or use on duplicate update record if your project has this requirement.

Answer 2

query for the max priority for the student then increment it with 1.
$queryMaxPriority = 'select max(priority) from flux_project_selection where id = STUDENT_ID;
$priority_no = $queryMaxPriority + 1;
i used this in some of my apps i developed.
Update
$priority = 'select count(priority) from flux_project_selection where id = STUDENT_ID and priority = PRIORITY';
if (count($priority>0)){
//send some error message in your page.
}