L’intersection de deux relations possédant un schéma identique produit une relation résultante. Cette dernière de même schéma que celles dont elle est issue contient l’ensemble des n-uplets communs aux deux relations.
Formalisme : R = INTERSECTION(Ra, Rb)
| Ra |
A |
B |
C |
| |
a |
b |
c |
| d |
e |
f |
| g |
h |
i |
| m |
n |
o |
| p |
q |
r |
| s |
t |
u |
|
| Rb |
A |
B |
C |
| |
a |
b |
c |
| g |
h |
i |
| j |
k |
l |
| p |
q |
r |
| v |
w |
x |
| y |
z |
a |
|
|---|
| INTERSECT(Ra, Rb) |
A |
B |
C |
| |
a |
b |
c |
| g |
h |
i |
| p |
q |
r |
|
|---|
Langage SQL :
SELECT * FROM Ra
INTERSECT
SELECT * FROM Rb;
'ou
SELECT A, B, C FROM Ra
WHERE A IN (SELECT A FROM Rb)
AND B IN (SELECT B FROM Rb)
AND C IN (SELECT C FROM Rb) ;