Database Reference
In-Depth Information
Note:
1.
These are binary operations and in each case, both relations
must have corresponding attributes that are defined on the
same domain.
2.
Union
and
intersect
are associative, but
minus
is not.
7.3.7 Division Statement
The
DIVIDEBY
statement is of the form
In this format, relation R1 contains [
m + n
] attributes and relation R2 has
n
attributes.
The operation of division is as follows:
•
Every attribute of R2 must be an attribute of R1.
•
The resulting relation will have remaining attributes of R1.
•
A tuple occurs in R1 DIVIDEBY R2 if it occurs in R1, concatenated
with every tuple in R2.
Example 6:
Figure
7-5
provides two illustrations that should help you gain insight
into the division operation. The first demonstrates how the division operation works; the
second demonstrates that the division operation is the opposite of the Cartesian product
operation.
Figure 7-5.
Illustrating the Division Operation
