A small remark:

Page 15, paragraph 3:

“Operation 5 is executed eight times, once for each distinct value in the column empno in the table emp after applying the filter imposed by the operation”

It seems to me that Operation 5 is executed exactly 8 times because of the filter imposed by Operation 3. So the filter of Operation 3 gets applied and only the rows satisfying it go into the filer of Operation 5. Which means “eliminate early” and somehow makes sence.

I think it is not a coinsidence that exactly 8 employees do not belong to department “SALES” – meaning they satisfy the filter of Operation 3. That’s why Operation 5 gets started 8 times – once for each of those employees.

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