Performance
  
  * virtual pivot table vs aggregate view
  
  * select * from pivot_table where attribute_001=X;
  
      X   rows  aggregate  virtual (first) virtual (second)
    ---   ---- ----------- -------------- ----------------
      0     0      3.4        0.5            0.1 seconds
      1     2      3.4        0.5            0.1
      2     2      3.4        0.5            0.1
      3     2      3.4        0.5            0.1
     10     3      3.4        0.5            0.2
     20     2      3.4        0.5            0.1
     30     2      3.4        0.5            0.1
     40     4      3.4        0.5            0.2
     50     1      3.4        0.5            0.1
    100     2      3.4        0.5            0.1
    200     3      3.4        0.5            0.2
    500     0      3.4        0.4            0.1