Joining 5 tables in SQL in a PHP function - php

Question

What I'm trying to return in a set: The lessonIDs associated to the userID and schoolID within a given startTime and endTime.
This is to be displayed on a calendar. I only want to display the lessons that are associated to the user viewing it for a selected school within the time range they are viewing on the calendar.
This data is just dummy data to show the table structure and data types.
Lesson Table:
lessonID roomFK startTime endTime
1 2 2014-08-01 13:00:00 2014-08-01 14:00:00
2 3 2014-08-01 13:00:00 2014-08-01 14:00:00
Room Table:
roomID schoolFK
1 1
2 1
3 2
4 2
School Table:
schoolID
1
2
User Table:
userID
1
2
3
Lesson/Teacher Junction Table:
lessonFK teacherFK
1 1
1 2
2 3
What I've tried:
function find_lessons_by_school_id_and_teacher_id_ranged_feed($school_id, $teacher_id, $start, $end) {
global $connection;
$school_id = mysqli_real_escape_string($connection, $school_id);
$teacher_id = mysqli_real_escape_string($connection, $teacher_id);
$start = mysqli_real_escape_string($connection, $start);
$end = mysqli_real_escape_string($connection, $end);
$start = strftime("%Y-%m-%d %H:%M:%S", $start);
$end = strftime("%Y-%m-%d %H:%M:%S", $end);
$query = "SELECT * ";
$query .= "FROM lesson ";
$query .= "JOIN room ON lesson.roomFK = room.roomID ";
$query .= "JOIN school ON room.schoolFK = school.schoolID ";
$query .= "JOIN user ON user.userID = junc_lesson_teacher.teacherFK ";
$query .= "JOIN junc_lesson_teacher ON junc_lesson_teacher.lessonFK = lesson.lessonID ";
$query .= "WHERE room.schoolFK = '{$school_id}' ";
$query .= "AND lesson.startTime >= '{$start}' ";
$query .= "AND lesson.endTime <= '{$end}' ";
$query .= "AND user.userID = '{$teacher_id}' ";
$query .= "ORDER BY lesson.roomFK ASC";
$set = mysqli_query($connection, $query);
return $set;
}
When I run this, mySQL complains about the query statement.
Any input on how to do this properly would be greatly appreciated! Thanks!

Answer 1

The order of your join operations is wrong. You've got to swap the last two ones. Instead of
$query .= "FROM lesson ";
$query .= "JOIN room ON lesson.roomFK = room.roomID ";
$query .= "JOIN school ON room.schoolFK = school.schoolID ";
$query .= "JOIN user ON user.userID = junc_lesson_teacher.teacherFK ";
$query .= "JOIN junc_lesson_teacher ON junc_lesson_teacher.lessonFK = lesson.lessonID ";
write
$query .= "FROM lesson ";
$query .= "JOIN room ON lesson.roomFK = room.roomID ";
$query .= "JOIN school ON room.schoolFK = school.schoolID ";
$query .= "JOIN junc_lesson_teacher ON junc_lesson_teacher.lessonFK = lesson.lessonID ";
$query .= "JOIN user ON user.userID = junc_lesson_teacher.teacherFK ";
because every table you use in a join must be introduced first. By your statement you can't use junc_lesson_teacher to join the user table, so you've got to join junc_lesson_teacher before you join user. Think of your tables as a chain without interrupts.

Answer 2

If you had a moderately sensible naming policy, that query might look like this...
$query = "
SELECT columns
, i
, actually
, want
FROM lesson l
JOIN room r
ON r.room_id = l.room_id
JOIN school s
ON s.school_id = r.school_id
JOIN lesson_teacher lt -- <-- NOTE TABLES SWAPPED AROUND
ON lt.lesson_id = l.lesson_id
JOIN user u
ON u.user_id = lt.teacher_id -- <-- SEE?
WHERE r.school_id = $school_id
AND l.startTime >= '$start'
AND l.endTime <= '$end'
AND u.user_id = $teacher_id
ORDER
BY l.room_id ASC;
";
$set = mysqli_query($connection, $query)
or die(mysqli_error($connection)); -- for development only

Answer 3

instead of
$query = "SELECT * ";
write all of required fields from all tables
$query = "SELECT lesson.roomFK,room.roomID,school.schoolID,room.schoolFK,user.userID,junc_lesson_teacher.teacherFK,junc_lesson_teacher.lessonFK,lesson.lessonID";