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Type:
Task
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Resolution: Duplicate
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Priority:
Major - P3
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None
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Affects Version/s: 5.0.26, 6.0.15, 7.0.9
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Component/s: None
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Labels:None
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Query Execution
Example:
db.foo.insertMany([
{ _id: 1, a: 1},
{ _id: 2, a: null},
{ _id: 3, b:1 }
])
db.foo.createIndex({"a":1})
db.foo.aggregate([{$match: { "a": {$gte: MinKey()}}}, {$group: {_id: "$a", c: {$sum:1}}}])
[ { _id: null, c: 2 }, { _id: 1, c: 1 } ]
db.foo.dropIndexes()
db.foo.createIndex({ "$**": 1 })
db.foo.aggregate([{$match: { "a": {$gte: MinKey()}}}, {$group: {_id: "$a", c: {$sum:1}}}])
[ { _id: null, c: 1 }, { _id: 1, c: 1 } ]
When using classic index filtering by $gte: MinKey() takes into account not existing fields and null value (and therefore the query can be even covered) having { _id: null, c: 2 }
When using wildcard indexes only the null values are taken into account and not the not-existing fields, therefore the query result is different compared to using classic index { _id: null, c: 1 } and the query cannot be covered.
- duplicates
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SERVER-37164 Incorrect query results on $gte null with sparse index
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- In Code Review
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