, .
, . , .
:
R rename A1,A2,,An as B1,B2, , Bn
A1,A2,,An R,
B1,B2, , Bn , .
. City(N, name) City(id, name).
ity rename N as id
, .
:
union
4.1. A B .
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1. , , . , A, B, . (1, )
2. , , A B .
. , .
, .
:
intersect
4.2. A B,
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, .
:
minus
4.3. A B,
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2- ( 1, , n) ( 1, , m) ( 1, , n, 1, , m) .
:
times
1. times .
2. , .
3. , .
4.5. A B .
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A C , A, , , C . C , A () .
where
4.6. 1200.
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.
A X,Y, ,Z, A, (X,Y,,Z) , (x,y,,z), , A X x, Y y, , Z z.
A [X,Y,...,Z]
. , .
4.7. .
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:
1) .
2) q- .
3) .
4) .
. (A times B) where .
1. .
2. , .
q - . , , q- q={<,³,>,£,}, q- (A times B) where X q Y.
A [ X q Y ] B
4.8. X B Y
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() ()
| . | Y | ||||
1 | 4 | 1 | 3 | |||
2 | 1 | 2 | 2 | |||
3 | 2 | 3 | 1 |
, .
A [ x ³ y ] B [, .]
. | . |
. - q , q(=).
[ x = y ] B
.
(A 1,, An, x 1,, xp) (x 1,, xp, B 1,, Bn) (A 1,, An, x 1,, xp, B 1,, Bn) (a 1,, an, x 1,, xp, b 1,, bm) , (a 1,, an, x 1,, xp) Î , (x 1,, xp, b 1,, bm)Î .
A join B
(A 1,, An, B 1,, Bm) (B 1,, Bm).
(A 1,, An) (a 1,, an) , (b 1,, bm)Î (a 1,, an, b 1,, bm)Î .
A devide by B.
. .
.