Database Reference
In-Depth Information
The union operator produces output from two relations R and S containing all the tuples of
R or S, or both R and S. Duplicate tuples are removed from the output
The difference operator produces output from two relations R and S in which output tuples
exist in R but not S
The intersection operator produces output from two relations R and S in which output
tuples exist both in R and S
A natural join is an equi-join of two relations R and S. One instance of each of the common
attributes in the output relation is projected out
4.15 RELATION SCHEME Definition
σ predicate (R)
π a
1
, . . ., a
n
(R)
RS
R - S
R S
R |><| S
It consists of relation name, and a set of attributes or field names or column names. Each
attribute has an associated domain.
Example 20 :
Example 21
:
