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Type:
Improvement
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Resolution: Unresolved
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Priority:
Major - P3
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None
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Affects Version/s: None
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Component/s: None
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Labels:
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Query Execution
Half of the generated GroupStage is
[{$group: {_id: null}}]
this is because the grammar rule is
IdExpression -> "_id: " Expression | "_id: null"
it makes Expression and null case equally weighted, and causing a lot of null cases are duplicated.
Similar to AddFieldsStage:
AddFieldsStage -> "{$addFields: {" AddFieldsList "}}" AddFieldsStage -> "{$addFields: {}}"