Declarative Query Processing 13
tuples before passing them to the next operator. Specifically, the Hash Join
operator in the figure passes only matching tuples for which employees earn
more than their managers. The result of this operator is a relation of all en-
gineers who earn more than their managers. This intermediate result is input
to the second Hash Join operator in the figure, which matches employees
and the corresponding departments (the Scan operator over Dept (alias D)
discards all departments with high budgets). This second Hash Join opera-
tor produces the list of all engineers who earn more than their managers and
work in low-budget departments, along with their department information.
This intermediate result is sorted by department cities ...