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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';

Evaluated via communication between RA tree nodes:

[Diagram:Pics/qproc/qtree.png]



Note: likely that projection is combined with join in PostgreSQL