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Pipelining Example

Consider the query: 

select s.id, e.course, e.mark
from   Student s, Enrolment e
where  e.student = s.id and
       e.semester = '05s2' and s.name = 'John';

which maps to the RA expression

Proj[id,course,mark](Join[student=id](Sel[05s2](Enr),Sel[John](Stu)))

which could represented by the RA expression tree

[Diagram:Pics/qproc/qtree0.png]