Question

I have a search page where I am trying to build a complex search condition on two tables which look something like:

Users
ID     NAME
1      Paul
2      Remy

…

Profiles
FK_USERS_ID   TOPIC      TOPIC ID
1             language   1
1             language   2
1             expertise  1
1             expertise  2
1             expertise  3
2             language   1
2             language   2

The second table Profiles, lists the “languages” or the “expertises” (among other stuff) of each user, and topic id is a foreign key to another table depending on the topic (if topic is “language”, than topic ID is the ID of a language in the languages table, etc…).

The search needs to find something like where user name LIKE %PAU% and the user “has” language 1 and has language 2 and has expertise 1 and has expertise 2.

Any help would be really appreciated! I am performing a LEFT JOIN on the two tables although I am not sure that is the correct choice. My main problem lies on the “AND”. The same user has to have both languages 1 and 2, and at the same time expertise 1 and 2.

I work in PHP and I usually try to avoid inner SELECTs and even joins, but I think an inner SELECT is imminent here?

Answer 1

You can accomplish this by building a set of users that matches the criterias from your profile tables, something like this:

SELECT FK_USERS_ID 
FROM Profiles 
WHERE topic='x' 
AND TOPIC_ID IN (1,2) 
GROUP BY FK_USERS_ID 
HAVING COUNT(1) = 2

Here you list your users that matches the topics you need. By grouping by the user id and specifying the amount of rows that should be returned, you can effectively say “only those that has x and y in topic z. Just make sure that the COUNT(1) = x has the same number of different TOPIC_IDs to look for.

You can then query the user table

SELECT ID 
FROM Users 
WHERE name like '%PAU%' 
AND ID IN (<insert above query here>)

You can also do it in a join and a derived table, but the essence should be explained above.

EDIT:
if you are looking for multiple combinations, you can use mysql’s multi-column IN:

SELECT FK_USERS_ID 
FROM Profiles 
WHERE (topic,topic_id) IN (('x',3),('x',5),('y',3),('y',6))
GROUP BY FK_USERS_ID 
HAVING COUNT(1) = 4

This will look for uses matching the pairs x-3, x-5, y-3 and y-6.

You should be able to build the topic-topic_id pairs easily in php and stuffing it into the SQL string, and also just counting the number of pairs you generate into a variable for using for the count(1) number. See http://www.mysqlperformanceblog.com/2008/04/04/multi-column-in-clause-unexpected-mysql-issue/ for performance talk using this approach.