mysql - access level for php -

i have 3 tables student, instructor, , admin, each 1 of them contains id, username, password, email , access_level. access_level student 1, instructor 2, , admin 3. want filter login different pages, each user direct different page. have been looking , searching answer unfortunately nothing me.

try :

if(valid($username,$password)>0){     //setcookie     //setsession     if(valid($username,$password)==1){         //redirect student page     }     elseif(valid($username,$password)==2){ //redirect instructor page     }     else{         //redirect admin page     }  } else{     //redirect login }