Ordering users with most matching user's skills - php

Question

I want to show recommended users to a user in descending order where skills match the most.
Issue is that I am storing skill in single field in this form
user_skill
musician,pop,singer
Note: this will be input musician,pop,singer..
so what I want to achieve I want to show users have all three skills at top,then those having two at last those having only one.
so out put will be like
**user_name skills**
sam musician,pop,singer
smith musician,pop,singer
ali musician,singer
nasira musicain,pop
siri musician
taylor pop
andrew singer
Can this be achieved by single mysql query?
If this not possible can this be done by php code.I don't want to change table structure as this will require lots of redo.
Thanks for your help.

Answer 1

You might be able to do with with SQL but the query would be so complex i probably wouldnt.
On the php side you could iterate over the result set and tally the skills for each user_name within a given set of skills you are looking for, and then just sort them:
$desired = explode(',', $input);
$users = array();
// i presume you have the query worked out to find users with any one of input
// skills attributed to them so lets say that $stmt is the PDO statement where you
// have executed that query
while (false === ($row = $stmt->fetch(PDO::FETCH_ASSOC))) {
$row['skills'] = explode(',', $row['skills']);
// assign an array containing only skills that were in your $input
// to $row['desired_skills']
$row['desired_skills'] = array_intersect($desired, $row['skills']);
$row['nb_desired_skills'] = count($row['desired_skills']);
$user[] = $row;
}
usort($users, function ($a, $b) {
return $b['nb_desired_skills'] - $a['nb_desired_skills'];
});
// now you can loop over $users and display the fields you need
However, the definition and attribution of these skills is a key part of you application, you should just normalize the tables now... its only going to become a larger refactor by putting it off.

Answer 2

I don't want to change table structure as this will require lots of redo.
I strongly (!) recommend you make a separate skills table, and link that to your users table using foreign keys. You will be infinitely thankful to yourself once your project gets even slightly more complex.
If you don't know how, I'm sure people on this site would help you with a script that does the conversion if you were to post another question.
MySQL
CREATE TABLE skills
(
name VARCHAR(64) NOT NULL,
user_id INT NOT NULL,
PRIMARY KEY (name, user_id),
FOREIGN KEY (user_id) REFERENCES users(id)
);
This way you can easily select users by most skills using a simple subquery (assuming you have a users table with an id column):
MySQL
SELECT *,
(SELECT COUNT(*)
FROM skills
WHERE user_id = u.id) AS num_skills
FROM users u
ORDER BY num_skills DESC;
So why would you take this approach instead of relying on PHP?
Creates minimal extra overhead in database,
significantly reduces chatter between database and webserver by not requiring to query the entire users table if you just want, for example, only the top 10 users,
enables more complex and varying queries in the future easily.
The following MySQL snippet queries only those users who have a given skill (for example, "singer"), then sorts them in descdending order based on number of skills. The query does not return users with zero skills:
MySQL
SELECT *,
(SELECT COUNT(*)
FROM skills
WHERE user_id = u.id
AND name = 'singer') AS num_skills
FROM users u
WHERE num_skills > 0
ORDER BY num_skills DESC;
Of course, you can also search for skills by id just replace the second part of the WHERE clause inside the subquery with AND id = 3, which will query those users, who have a skill with ID of 3.
The next step towards a more optimal database would be creating a real skills table, which stores only the skills that you have registered in your database, and a user_skills table, that links it and the users table together.
This would enable you to significantly reduce database size on the long run, and be able to run complex but 'clean' queries that do not depend on the webserver.