Multi-Join Query, Pivot? Troubles - mysql

Question

Thank you in advance for anyone who helps with this. I know i've seen this done before without too much pain but cant seem to find the solution
My database looks something like:
`tbl_user:
----------
id ( pkey )
email
fName
lName
tbl_userSparseType:
-------------------
id ( pkey )
varName
displayName
tbl_userSparse:
---------------
id ( pkey )
value ( Value of Sparse Type )
user_id ( => tbl_user.id )
userSparseType_id ( => tbl_userSparseType.id )
with sample data:
tbl_user:
(id, email, fName, lName)
1 Bob#example.com Billy Bob
2 Betty#example.com Betty Sue
3 Beam#example.com Jim Beam
tbl_userSparseType:
(id, varName, displayName)
1 fullName Full Name
2 dayPhone Day Phone
3 nightPhone Night Phone
4 cellPhone Cell Phone
5 homeAddr Home Address
tbl_userSparse:
(id, value, user_id, userSparseType_id)
1 Billy John Bob 1 1
2 James B. Beam 3 1
3 123-234-3456 1 2
4 234-345-4567 1 4
5 24 Best st. 2 5
6 456-567-6789 3 3
I tried doing two left joins, but this gave me a tbl_user row for each sparse entry like:
(id, email, fName, lName, displayName, value)
1,"Bob#example.com","Billy","Bob","Full Name","Billy John Bob"
1,"Bob#example.com","Billy","Bob","Day Phone","123-234-3456"
1,"Bob#example.com","Billy","Bob","Cell Phone","234-345-4567"
And despite a few 45 or so minute sessions of looking, I cant find a way to get something more like the following without explicitly naming the columns, I need a dynamic way to only pull all display names that apply to the subset of tbl_user rows being queried:
WHERE tbl_user.id IN (1,2)
id | email | fName | lName | Full Name, | Day Phone | Cell Phone |
Home Address
-------------------------------------------------------------------------------------------------------
1 | Bob#example.com | Billy | Bob | Billy John Bob | 123-234-3456 | 234-345-4567 |
2 | Betty#example.com | Betty | Sue | | | | 24 Best St.
Thanks again in advance, I'm hoping this can be done without too much fuss. :\

Answer 1

Unfortunately MySQL does not have a PIVOT function which is basically what you are trying to do. So you will need to use an aggregate function with a CASE statement. If you know the number of columns, then you can hard-code the values:
select u.id,
u.email,
u.fname,
u.lname,
max(case when t.displayname = 'Full Name' then us.value end) FullName,
max(case when t.displayname = 'Day Phone' then us.value end) DayPhone,
max(case when t.displayname = 'Cell Phone' then us.value end) CellPhone,
max(case when t.displayname = 'Home Address' then us.value end) HOmeAddress
from tbl_user u
left join tbl_userSparse us
on u.id = us.user_id
left join tbl_userSparseType t
on us.userSparseType_id = t.id
where u.id in (1, 2)
group by u.id, u.email, u.fname,u.lname;
See SQL Fiddle With Demo
Now if you want to perform this dynamically, meaning you do not know ahead of time the columns to transpose, then you should review the following article:
Dynamic pivot tables (transform rows to columns)
Your code would look like this:
SET #sql = NULL;
SELECT
GROUP_CONCAT(DISTINCT
CONCAT(
'max(case when t.displayname = ''',
t.displayname,
''' then us.value end) AS ',
replace(t.displayname, ' ', '')
)
) INTO #sql
FROM tbl_userSparse us
left join tbl_userSparseType t
on us.userSparseType_id = t.id;
SET #sql = CONCAT('SELECT u.id, u.email, u.fname, u.lname, ', #sql, '
from tbl_user u
left join tbl_userSparse us
on u.id = us.user_id
left join tbl_userSparseType t
on us.userSparseType_id = t.id
where u.id in (1, 2)
group by u.id, u.email, u.fname, u.lname');
PREPARE stmt FROM #sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;
See SQL Fiddle with Demo