Login failed in my code after inserting proper login details (i.e username and password), code in php and jquery

Question

I have following code (php and jquery) for Login for Student and Teacher (using same form for both access). In my system the admin can create Student and Teacher. Once created,

Answer 1

I think the problem is here;

if( $count_stu > 0 ) { 
    //$_SESSION['id']=$row_student['student_id'];// mistake
    $_SESSION['id']=$row_stu['student_id'];
    echo 'true';
}else if( $count_tea > 0 ) { 
    //$_SESSION['id']=$row_teacher['teacher_id'];// mistake
    $_SESSION['id']=$row_tea['teacher_id'];
    echo 'true_teacher';
}
else{ 
    echo 'Wrong Username Or Password';
}

I agree with @Drew Pierce, you should consider using pdo or mysqli.