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I couldn't find that example right now but there is a similar line in the main example on the prql-lang.org homepage: aggregate { average total,

• aidos 3y ago
  Gotcha. The thing that’s not immediately clear from the syntax is which columns I’m getting out as a final result of my query. I guess the last select you ran + any derived ones since then?
  • snthpy 3y ago
    That's right. It can be a bit hard to keep track of but the rules are quite simple. You start with all the columns from a `from`, then any `derive` just adds columns. A `select` restricts the columns to those selected and a `group + aggregate` replaces the columns with those from the `group` + those from the `aggregate`. I once tabled a proposal whether each query should be forced to end with a `select` to make the final column list explicit. This could be generated by the compiler. It was felt that that wasn't necessary though and would also be somewhat arbitrary since you also need to know what columns are available at each previous step of the pipeline if you want to be able to make modifications. As the tooling improves, you could perhaps be shown the current list of columns as you hover over each line?
    • aidos 3y ago
      There’s nothing stopping people from using their own convention of selecting early to grab the stuff they need and selecting again right at the end to be explicit about what they want. Like select *, it’s better to just be explicit.