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Type:
Bug
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Resolution: Fixed
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Priority:
Major - P3
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Affects Version/s: None
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Component/s: None
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None
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Query Execution
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Fully Compatible
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ALL
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QE 2026-01-19, QE 2026-01-05, QE 2025-12-22
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None
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None
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None
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None
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None
This:
db.adminCommand({setParameter: 1, internalEnableJoinOptimization: true});
db.foo.drop();
db.bar.drop();
db.foo.insert({f: 1, g: 1});
db.bar.insert({a: 1});
db.foo.aggregate([
{
"$project" : {
"f" : "$g",
"g" : 1,
}
},
{
"$lookup" : {
"from" : "bar",
"localField" : "_id",
"foreignField" : "_id",
"as" : "y"
}
},
{
"$unwind" : "$y"
},
]);
results in this:
MongoServerError[Location4822820]: duplicate field: 4
Not reproducible with internalEnableJoinOptimization set to false.
Not reproducible with featureFlagSbeFull alone. internalEnableJoinOptimization is required.