MySQL - subquery or joining multiple rows - mysql

Question

I got a little struggle with my mysql query. Maybe someone can help me.
Tables:
contacts:
|id|phone|first_name|last_name|email|company|
custom_values:
|id|c_id|custom_field_id|value|
The table custom_values got different custom_field_ids
id 4 = mobile
id 5 = fax
id 20 = 2nd phonenumber
The current query gives me all information from my contacts table.
concat(contacts.first_name, ' ', contacts.last_name, ' - ', contacts.company) as displayname, contacts.phone, contacts.last_name, contacts.first_name, contacts.company, contacts.email
from contacts
Now I want to add the information from the custom_values table to the query above.
Is it possible to add 3 rows, that adds me mobile, fax and the 2nd phonenomber to every contact?
I tried with the next query, but that doesn´t work.
SELECT
concat(contacts.first_name, ' ', contacts.last_name, ' - ', contacts.company) as displayname, contacts.phone, contacts.last_name, contacts.first_name, contacts.company, contacts.email,custom_values.value as mobile
from custom_values
join contacts on custom_values.customized_id = contacts.id
where custom_values.custom_field_id=4
thanks guys.

Answer 1

If you want additional rows, then your approach is fine. However, I think you want additional columns, not additional rows.
One approach is multiple LEFT JOIN:
select concat(c.first_name, ' ', c.last_name, ' - ', c.company) as displayname,
c.phone, c.last_name, c.first_name, c.company, c.email,
cvm.value as mobile,
cvf.value as fax,
cvp2.value as second_phone
from contacts c left join
custom_values cvm
on cvm.customized_id = c.id and
cvm.custom_field_id = 4 left join
custom_values cvf
on cvf.customized_id = c.id and
cvf.custom_field_id = 5 left join
custom_values cvp2
on cvp2.customized_id = c.id and
cvp2.custom_field_id = 20;