Question

I’ve recently been required to input more information from my database and I’ve just LEFT JOIN to help me, it works almost perfectly(it does actually get the right field from the other table) but my WHERE clause is nullified giving the user access to both tables without the restriction of my where clause.

MySQL doesn’t crap out any errors, so I’m assuming it’s something to do with my where clause or something happened in the join.

SELECT * FROM students 
LEFT JOIN courses ON students.appliedforCourse = courses.idNumber 
WHERE 
    students.telephone LIKE '%$var' 
    OR students.email LIKE '%$var' 
    OR students.address like'%$var%' 
    OR (CONCAT(students.firstName,' ',students.lastName) LIKE '%$var%')
    AND addedBy ='$userid'
LIMIT $s,limit

Answer 1

The query itself is correct (although really inefficient due to ORs and % % [ indexes will not be used] ).
I would suggest to echo the query, are you sure that $var is evaluated correctly ? Try to run the query directly in mysql (via phpmyadmin for example or using console).