Mysql search, order according to priority - mysql

Question

I decided that I wanted a search field on my website, the thing is I don't really have any knowledge about search algorithms. The search box works like you can enter any number of names(username, firstname, lastname) or emails separating each by a space. So I came up with the following using codeigniter's active record class (it's very simple):
$emails = FALSE;
$names = FALSE;
foreach($search_array as $value){
if(valid_email($value)){
$emails[] = $value;
} else{
$names[] = $value;
}
}
if($emails){
$this->db->where_in('email', $emails);
if($names){
$this->db->or_where_in('username', $names);
$this->db->or_where_in('firstname', $names);
$this->db->or_where_in('lastname', $names);
}
} else{
if($names){
$this->db->where_in('username', $names);
$this->db->or_where_in('firstname', $names);
$this->db->or_where_in('lastname', $names);
}
}
$this->db->select('id, username, firstname, lastname');
$query = $this->db->get('users');
if($query->num_rows() > 0){
return $query->result();
}
return FALSE;
What this code does is running a bunch of where statements and then simply sending it all back.
Perhaps I could clean up the if-statements and how the email works, but that's not the point. This code works perfectly (at least with a very small database :P) but I want it to do more:
Right now you need to enter the correct name or email to get any good result. If your almost right it would be nice to get some suggestions but that I probably can figure that out by myself doing some LIKE.
I want to sort the whole result array, and here is where I'm stumbling. Since both the email and the username is unique I want a search to display using the following priorities:
Email
Username
Firstname + Lastname
Firstname
Lastname
Well for the time being I don't really care about for example Email+username+firstname+lastname since I believe that would be way to overwhelming :P
I did found this topic Search query, 'order by' priority but since I don't know which is what in my search it didn't really help me but perhaps I could use something similar?
Anyway you guys know a way to solve the priority problem? Have I perhaps missed some major functions that could help? And what will happen when my database goes big? ;)
Thanks for all help!

Answer 1

You can do:
ORDER BY email != 'value',
username != 'value',
firstname != 'value' AND lastname != 'value',
firstname != 'value',
lastname != 'value'
If the expression is false (meaning they are the same) then it's equal to 0 and will sort higher than an expression that is true (meaning they are different) which equals 1 and sorts after a 0.
If you find the != confusing then this is the same thing:
ORDER BY email = 'value' DESC,
username = 'value' DESC,
firstname = 'value' AND lastname = 'value' DESC,
firstname = 'value' DESC,
lastname = 'value' DESC