MySQL query to convert normalized data into single row - mysql

Question

I'm trying to create a query to format content from normalized tables into a single row.
What I would like is something like this with a single row for each contact:
Name Mobile Office Home
--------------- ----------- ---------- ----------
Fred Flintstone 123-456-7890 234-567-8901 789-012-3456
Barney Rubble 456-789-0123 678-901-2345
Wilma Flintstone 567-890-1234 789-012-3456
What I am getting from my latest query is this, with multiple rows per contact:
Name Phone Phone_Type
--------------- ------------ -----------
Fred Flintstone 123-456-7890 Mobile
Fred Flintstone 234-567-8901 Office
Fred Flintstone 789-012-3456 Home
Barney Rubble 456-789-0123 Mobile
Barney Rubble 678-901-2345 Home
Wilma Flintstone 567-890-1234 Mobile
Wilma Flintstone 789-012-3456 Home
Here are the tables involved (simplified):
contacts
----------
contact_id
name
link_contact_phonenumbers
-------------------------
contact_id
phone_number_id
phone_numbers
-------------
phone_number_id
phone_number
type_id
ref_phone_types
---------------
type_id
name
Here is what I have so far:
SELECT
cn.name as Name,
concat( left(ph.phone_number,3) , "-" , mid(ph.phone_number,4,3) , "-", right(ph.phone_number,4)) as Phone,
pt.name as Phone_Type
FROM
contacts cn
LEFT JOIN link_contact_phonenumbers lp ON lp.contact_id = cn.contact_id
LEFT JOIN phone_numbers ph ON ph.phone_number_id = lp.phone_number_id
LEFT JOIN ref_phone_types pt ON pt.type_id = ph.type_id
I looked at using GROUP_CONCAT() function, but that pulls all the content into a single column. I need them to go into their own columns.
I've been looking into subqueries combined with IF() but haven't figured it out yet.
Is there a way to do this in pure SQL?

Answer 1

It sounds like you can accomplish what you are looking for with a few joins:
Select a.name, c.phone_number, d.phone_number, e.phone_number from contacts a
left join link_contact_phonenumbers b on a.contact_id = b.contact_id
left join phone_numbers c on b.phone_number_id = c.phone_number_id and c.type_id = "whatever id is mobile"
left join phone_numbers d on b.phone_number_id = d.phone_number_id and d.type_id = "whatever id is office"
left join phone_numbers e on b.phone_number_id = e.phone_number_id and e.type_id = "whatever id is home"
I do not know if this is the most efficient way, I also don't have a database to test with right now so it might be off, but it should point you in the right direction. Also might have to group by a.name in case the first join adds multiple rows.

Answer 2

Here is one solution for others that will find this in the future:
SELECT
cn.name as Name,
MAX(CASE WHEN pt.type_id = '1' THEN ph.phone_number ELSE NULL END) as Mobile,
MAX(CASE WHEN pt.type_id = '2' THEN ph.phone_number ELSE NULL END) as Office,
MAX(CASE WHEN pt.type_id = '3' THEN ph.phone_number ELSE NULL END) as Home
FROM
contacts cn
LEFT JOIN link_contact_phonenumbers lp ON lp.contact_id = cn.contact_id
LEFT JOIN phone_numbers ph ON ph.phone_number_id = lp.phone_number_id
LEFT JOIN ref_phone_types pt ON pt.type_id = ph.type_id
GROUP BY cn.contact_id
Found this solution here: How to Denormalize a Normalized Table Using SQL
I'm not sure if this is the most efficient, but it works.