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  1. Core Server
  2. SERVER-59159

$min/max window function null semantics are different than their accumulator counterparts

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    • Type: Icon: Bug Bug
    • Resolution: Fixed
    • Priority: Icon: Major - P3 Major - P3
    • 5.2.0, 5.0.4
    • Affects Version/s: None
    • Component/s: None
    • Labels:
      None
    • Minor Change
    • ALL
    • v5.1, v5.0
    • Hide 
      coll.drop();
coll.insert([{a: 1}, {a: null}]);
let results =
    coll.aggregate([
            {
                $setWindowFields: {
                    sortBy: {a: 1},
                    output: {
                        docs: {$push: "$a", window: {documents: [-1, 1]}},
                        min: {$min: "$a", window: {documents: [-1, 1]}},
                    }
                }
            }
        ])
        .toArray();
      Show
      coll.drop(); coll.insert([{a: 1}, {a: null }]); let results = coll.aggregate([ { $setWindowFields: { sortBy: {a: 1}, output: { docs: {$push: "$a" , window: {documents: [-1, 1]}}, min: {$min: "$a" , window: {documents: [-1, 1]}}, } } } ]) .toArray();
    • QE 2021-11-01

      The $min/max accumulators specifically throw out nullish values, whereas they are kept in a multiset for window functions. The behavior may end up being correct for $max since nulls will generally sort before other types, but for $min we will always return null.

            Assignee:
            mihai.andrei@mongodb.com Mihai Andrei
            Reporter:
            nicholas.zolnierz@mongodb.com Nicholas Zolnierz
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              Created:
              Updated:
              Resolved: