I was just wondering what the purpose of this lab is?
Determine the approach that satisfies the following question in the most efficient manner:
Find the list of all possible distinct destinations, with at most one layover, departing from the base airports of airlines that make part of the “OneWorld” alliance. The airlines should be national carriers from Germany, Spain or Canada only. Include both the destination and which airline services that location. As a small hint, you should find 158 destinations.
Considering, that only have one query seems to hit the target count (per the hint), that tends to make answering the question straight forward.
So what determines efficient in terms of this question, since I assuming that is the real point of the question? Use of indexes (of which there are none that I can see of any use by any of the queries). The lowest number of records accessed, during the processing of each of the pipelines.
So if the lesson of the lab, is to monitor the count of records through the various pipelines, and therefore highlighting the need to consider how you approach the construction of the pipeline. It would worth suggesting in the lab description, that the student breaks each pipeline apart, and counts the the records acquired at each stage.
Pipeline 1 = Record count
615 -> 615 -> 3 -> 3 -> 3 -> 2785 -> 450
Personally I thought the very last paragraph in the detailed answer is worth knowing.