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Assigned Teams:

Query Optimization
Operating System:
ALL
Steps To Reproduce:
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1: Create a new empty collection

2: Run the sample aggregation

[ { $count: "total" }, ]

3: Notice that it does not return anything. Expected result:

{ "total": 0 }

4: Add an object to the collection

5: Run the aggregation again

6: Returns an expected result of:

{ "total": 1 }
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1: Create a new empty collection 2: Run the sample aggregation [ { $count: "total" }, ] 3: Notice that it does not return anything. Expected result: { "total" : 0 } 4: Add an object to the collection 5: Run the aggregation again 6: Returns an expected result of: { "total" : 1 }

I was using the aggregation stage $count and noticed that if the input dataset was empty that $count does not return anything.

I was expecting it to return 0.

related to

SERVER-54958 Empty result when counting from empty collection in aggregation