Question 16

${\sigma }_{A\ne B}(E)\text{ est une abreˊviation pour }E-{\sigma }_{A=B}(E),\text{ ouˋ }A,B\in \text{sorte}(E)$

On définit $\text{VARIANT}={\pi }_{\{W\#,Product,Color\}}(STOCK)$

${\pi }_{\{Product\}}({\sigma }_{Color1\ne Color2}({\rho }_{Color\to Color1}(VARIANT)\bowtie {\rho }_{Color\to Color2}(VARIANT)))$

@allow <>
% base de données question 4
@let WAREHOUSES = @relation [W#, Address, City]{
  < D1, "6, Rue de l’Eglise", Mons     >
  < D2, "18, Place du Parc",  Mons     >
  < D3, "18, Place du Parc",  Chimay   >
  < D4, "5, Avenue Louise",   Enghien  >
}
 
@let STOCK = @relation [W#, Product, Color, Qty]{
  < D1, hinge,   yellow,  200 >
  < D1, hinge,   blue,    150 >
  < D2, lock,    blue,    100 >
  < D2, hinge,   yellow,  200 >
  < D2, handle,  red,     100 >
  < D4, hinge,   red,     150 >
  < D4, lock,    red,     600 >
}
 
@let VARIANT = @project {W#, Product, Color} STOCK
@print VARIANT
 
@let result = @project {Product} (@select {Color1<>Color2} (
	@rename {Color: Color1} VARIANT
    @join
    @rename {Color: Color2} VARIANT
    )
)
 
@print result