PERSONNE | ||
Nom | Age | Ville |
Marc | 29 | Paris |
Catherine | 32 | Lyon |
Sophie | 54 | Paris |
Claude | 13 | Montpellier |
Serge | 40 | Lyon |
R | |
A | B |
a | b |
a | f |
c | b |
d | e |
S | |
B | C |
b | c |
e | a |
b | d |
g | b |
R S | ||
A | B | C |
a | b | c |
a | b | d |
c | b | c |
c | b | d |
d | e | a |
sigmaA=C(rhoB/B'(R) × S) | |||
A | B' | B | C |
a | b | e | a |
a | f | e | a |
c | b | b | c |
d | e | b | d |
R semijoin S | |
A | B |
a | b |
c | b |
d | e |
|
piA,B(R S) | |
A | B |
a | b |
c | b |
d | e |
piB,C(R S) | |
B | C |
b | c |
b | d |
e | a |