23
Semijoins in Distributed Databases
•Semijoins are used in distributed databases
. .
.
. .
.
Name
SSN
Dname
. .
.
. .
.
Age
SSN
Employee
Dependents
network
Employee ⋈ssn=ssn (s age>71 (Dependents))
T = P SSN s age>71 (Dependents)
R =
Employee ⋉
T
Answer =
R ⋈
Dependents
