Pivoting EAV

If you are responsible for designing a data model and just consider to invent again and create this fine generic entity attribute value structure, maybe you should consider attending some teaching about the issue. For example some available soon by C.J. Date in and near Finland.

Well maybe you have a EAV model that you have to deal with. Example

SQL> create table eav as
  2  select 1 e, 'first' a, 'Timo' v from dual union all
  3  select 1 e, 'last' a, 'Raitalaakso' v  from dual union all
  4  select 1 e, 'nic' a, 'Rafu' v  from dual union all
  5  select 2 e, 'first' a, 'John' v  from dual union all
  6  select 2 e, 'last' a, 'Doe' v from dual
  7  ;

Table created.

SQL> select * from eav;

         E A     V
---------- ----- -----------
         1 first Timo
         1 last  Raitalaakso
         1 nic   Rafu
         2 first John
         2 last  Doe

You should not query it in a basic case using joins. Most possibly you have tens of joins to the same table.

SQL> select la.e, fi.v firs, la.v las
  2    from eav la, eav fi
  3   where la.e=fi.e
  4     and fi.a='first'
  5     and la.a='last'
  6  ;

         E FIRS        LAS
---------- ----------- -----------
         1 Timo        Raitalaakso
         2 John        Doe

It is a pivot you want to do.

SQL> select e, firs, las
  2    from eav
  3    pivot (max(v) for a in ('first' as firs, 'last' as las))
  4  ;

         E FIRS        LAS
---------- ----------- -----------
         1 Timo        Raitalaakso
         2 John        Doe

With the pivot you get the nullable columns also easier without filtering out the whole entity

SQL> select e, firs, las, ni
  2    from eav
  3    pivot (max(v) for a in ('first' as firs, 'last' as las, 'nic' as ni))
  4  ;

         E FIRS        LAS         NI
---------- ----------- ----------- -----------
         1 Timo        Raitalaakso Rafu
         2 John        Doe

Maybe you do not have 11g features available.

SQL> select e
  2       , max(case when a = 'first' then v end) firs
  3       , max(case when a = 'last' then v end) las
  4    from eav
  5   group by e
  6  ;

         E FIRS        LAS
---------- ----------- -----------
         1 Timo        Raitalaakso
         2 John        Doe

And the best thing to do with it might be.

SQL> drop table eav purge;

Table dropped.