SQL to fetch data using column values from one table as columns of another table - sql

Question

I have these two tables:
Org_Extra_Attr
org_id attr_name attr_path
1 desk_name str1
1 citizen bool1
2 perm_user bool1
3 skype_id str1
3 twitter str2
User_Attr_Values
org_id user_id str1 str2 str3 str4 bool1 bool2 bool3 bool4
1 1 b1d07 null null null 1 null null null
1 2 b2d01 null null null 0 null null null
2 3 null null null null 1 null null null
2 4 null null null null 1 null null null
3 5 sam_sky sam_twt null null null null null null
3 6 tom_sky tom_twt null null null null null null
So, the thing here is each org.can define max.of 4 extra attributes of type String and Boolean each, the Org_Extra_Attr table is like meta-data. For example org_id 1 has defined desk_name which will be str1's value for its users, whereas org_id 3 has skype_id which will be str1's value for its users.
This might be a bad design, but for now, I need to get users attribute names and values for a given org_id. Like for org_id = 1, I need a SQL query result(not a third table) like below:
user_id attr_name val
1 desk_name b1d07
1 citizen 1
2 desk_name b2d01
2 citizen 0
For org_id = 3
user_id attr_name val
5 skype_id sam_sky
5 twitter sam_twt
6 skype_id tom_sky
6 twitter tom_twt

Answer 1

Something like this
select
t2.user_id,
t1.attr_name,
CASE
WHEN t1.attr_path='str1' then t2.str1
WHEN t1.attr_path='str2' then t2.str2
WHEN t1.attr_path='str3' then t2.str3
WHEN t1.attr_path='str4' then t2.str4
WHEN t1.attr_path='bool1' then t2.bool1
WHEN t1.attr_path='bool2' then t2.bool2
WHEN t1.attr_path='bool3' then t2.bool3
WHEN t1.attr_path='bool4' then t2.bool4
END attr_value
FROM org_Extra_attr t1 inner join User_Attr_Values t2
on t1.org_id = t2.org_id
where t1.org_id=1

Answer 2

This is not an answer, but too long for a comment
That is a bad data model. You should not store column names in your tables.
What you could have instead is:
Org_Attr (PK = org_id + attr_no)
org_id attr_no attr_name type
1 1 desk_name STRING
1 2 citizen BOOL
2 1 perm_user BOOL
3 1 skype_id STRING
3 2 twitter STRING
Org_Attr_User (PK = org_id + attr_no + user_id)
org_id attr_no user_id value
1 1 1 b1d07
1 1 2 b2d01
1 2 1 1
1 2 2 0
2 1 3 1
2 1 4 1
3 1 5 sam_sky
3 1 6 tom_sky
3 2 5 sam_twt
3 2 6 tom_twt
With such a model data integrity would be guaranteed and querying, too, would be simple:
select oau.user_id, oa.attr_name, oau.value
from Org_Attr oa
join Org_Attr_User oau using (org_id, attr_no)
where org_id = 1;