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.
PRODUCTS
|
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N D1,D2, . Dn (), R N- <d1,d1,...dn>, d1 D1 . D1,D2,..Dn R.
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, .
DRIVERS
COMPANY | DRIVER |
, , . .
. (primary key) (foreign key) .
, .
.
..
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|
|
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SELLERS
ID | SELLER |
OOO | |
, ID , PRODUCTS.
. Ÿ , PRODUCTS, PRODUCTS.
, , , , , .
PRODUCTS ID PRICE.
:
π(ID, PRICE) PRODUCTS
:
ID | PRICE |
, , . .
90.
:
σ(PRICE>90) PRODUCTS
ID | NAME | COMPANY | PRICE |
. 90 ID 300:
σ(PRICE>90 ^ ID<300) PRODUCTS
ID | NAME | COMPANY | PRICE |
. , .
, 110.
πCOMPANYσ(PRICE<100) PRODUCTS
COMPANY |
, , . . .
PRODUCTS SELLERS.
:
PRODUCTS × SELLERS
, ID. , .
, ID<235
( )
PRODUCTS.ID | NAME | COMPANY | PRICE | SELLERS.ID | SELLER |
OOO | |||||
OOO |
90. ID , ID SELLER, :
|
|
π(SELLER) σ(RODUCTS.ID=SELLERS.ID ^ PRICE<90) PRODUCTS × SELLERS
:
SELLER |
. , , . , PRODUCTS SELLERS, ID.
. , . PRODUCTS.ID SELLERS.ID.
PRODUCTS SELLERS .
PRODUCTS.ID | NAME | COMPANY | PRICE | SELLERS.ID | SELLER |
OOO | |||||
, , ( PRODUCTS ID SELLERS ID), ID.
:
PRODUCTS ⋈ SELLERS;
:
PRODUCTS.ID | NAME | COMPANY | PRICE | SELLER |
OOO | ||||
.
, , .
, , .
, , , .
. .
Introduction to Databases Jennifer Widom, Stanford University
: http://habrahabr.ru/post/145381/