Make SQL selection from nested arrays - php

Question

I am trying to make a selection based on a nested array I get from a prior selection.
Here is where I make my first selection:
$coursequery = "
SELECT
courseID
FROM enrollments
WHERE
studentID = '$userid'
";
try
{
$stmt = $db->prepare($coursequery);
$result = $stmt->execute();
}
catch(PDOException $ex)
{
die("Failed to run query: " . $ex->getMessage());
}
$rows = $stmt->fetchAll();
$_SESSION['studentcourses'] = $rows;
This gets all the courseID's in the following format:
Array ( [0] => Array ( [courseID] => 6 ) [1] => Array ( [courseID] => 7 ) )
and I want to be able to access these ID's for selecting information from a different table. I've started by trying to use a for loop to grab all the "course information" depending on the ID.
for($i = 0; $i < $count; $i++) {
$coursequery = "
SELECT
*
FROM courses
WHERE courseID = '$studentcourses[$i]'
";
try
{
$stmt = $db->prepare($coursequery);
$result = $stmt->execute();
}
catch(PDOException $ex)
{
die("Failed to run query: " . $ex->getMessage());
}
$row = $stmt->fetchAll();
$_SESSION['studentcourseinfo'] = $row;
}
Any help would be greatly appreciated in accomplishing this!

Answer 1

You can accomplish this with one SQL query thus eliminating all these loops
SELECT
*
FROM courses
INNER JOIN enrollments ON
enrollments.courseID = courses.courseID
AND enrollments.studentID = '$userid'
WHERE 1

Answer 2

you can use same array in query, can use implode function
$coursequery = "SELECT * FROM courses
WHERE courseID IN (" . implode(",", $studentcourses) . ");";
As long as you change the output format
Array (6, 7)
where 6 and 7 would be the id of the courses
Also in you code have mistake in rewrite var $_SESSION['studentcourseinfo'] = $row; these overwriting the same variable at a time