Performance
  
  * virtual pivot table vs self-join view
  
    Queries were 5-10 times slower using the self-join view.
  
  * sample queries :
  * select id,attribute_001,attribute_002 from pivot_table
       where attribute_001 < 200 order by id;
  * select * from pivot_table where attribute_001=339 and attribute_002 > 0;
  * select id,attribute_001,attribute_002 from pivot_table
    where (attribute_001 between 100 and 900)
      and (attribute_002 between 300 and 900)
      and (attribute_003 < 800 or attribute_003 > 900) order by id;
  
    rows self-join view virtual pivot table
    ---- -------------- -------------------
       0    6.7         0.5 seconds
       2    6.8         0.4
       5   18.8         0.4
      12    8.0         0.6
      21    8.9         1.1
      42    9.0         0.8
     494   35.8         2.7