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Query Execution (cont)

Example of query translation: 

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

maps to

πname,id,course,mark(Stu ⋈e.student=s.id (σsemester=05s2Enr))

maps to 

Temp1  = BtreeSelect[semester=05s2](Enr)
Temp2  = HashJoin[e.student=s.id](Stu,Temp1)
Result = Project[name,id,course,mark](Temp2)