Row Denormalizer / Aggregated row per person - mysql

Question

I´m trying to denormalize some data in a table, but I cannot do it because I do not find the way to do it right way in mysql.

Table:person_attribute

Attribute_ID Attribute
------------  ---------
1            Person Name
2            Person Age
3            Person Gender
.
.
.
34           Phone Number

34 attributes as if now, but it is subject to change. ie i may get additional attributes also.

Table:person_data

Person ID fk_Attribute_ID Attribute_Value
--------- --------------- -------------
1          1              Max
1          2              55
1          3              male  
2          1              John
2          2              20
2          3              male  

Excepted Output:

Person ID Person Name Person Age Person Gender
--------- ----------- ---------- -------------
1           Max           55          male
2           john          20          male

My solution:

Select 
Person ID, 
case when fk_Attribute_ID = ( select Attribute_ID from    person_attribute where Attribute_ID = 1) then Attribute_Value end as Person Name,case when fk_Attribute_ID = ( select Attribute_ID from    person_attribute where Attribute_ID = 2) then Attribute_Value end as Person Age,case when fk_Attribute_ID = ( select Attribute_ID from    person_attribute where Attribute_ID = 3) then Attribute_Value end as Person Gender From person_attribute left join on person_data (Attribute_ID  = fk_Attribute_ID)

Person ID Person Name Person Age Person Gender
--------- ----------- ---------- -------------
1           Max           null          null
1           null          55            null
1           null          null          male
2           john          null          null
2           null          20            null
2           null          null          male

Please help me with excepted output. Thanks

Answer 1

It's a good idea to do this. This is not even denormalization; the resulting table is still normalized (ie no redundance etc.).

What you want is an aggregated row per person:

select 
  person_id,
  max(case when fk_attribute_id = 1 then attribute_value end) as person_name,
  max(case when fk_attribute_id = 2 then attribute_value end) as person_age,
  ...
from person_data
group by person_id;

Of course you need to know all attributes to build this query.