27



27


_ _
1 1 5
1 2 3
1 105 0.01
2 1 50

27 __

, , :

  1. R1(_,_,)= __[>90]. ( ).
  2. R2(_) = R1[_]. ( ).
  3. R3(_,)= R2[_=_]. ( )
  4. () = R3[]. ( ).

SQL : SELECT . FROM , __ WHERE ._=__._ AND __.>90;