Is there a way to write a nested query in mongoDB? - mongodb

Question

I an new to mongoDB and I am trying to achieve below SQL query equivalent in mongoDB
SELECT ROUND((SELECT COUNT() FROM INFODOCS WHERE ML_PRIORITY = HIGH AND PROCESSOR_ID = userid)
/ (SELECT COUNT() FROM INFODOCS WHERE PROCESSOR_ID = userid) * 100)
AS EFFORTS FROM DUMMY;
EFFORTS = Total High Priority Infodocs / Total Infodocs for a given Processor
I tried to write an aggregation pipeline using $match, $group, $count but the issue is once I get an output for one subquery i did not find anyway how can i compute another subquery and finally use the outputs of both subquery to determine the final result.

Answer 1

The mongo-y way would not to execute two different queries to get the 2 different counts, but to do a sum it dynamically with one query.
You can achieve this in many different ways, here is an example how to use $cond while $grouping to do a conditional sum.
db.collection.aggregate([
{
$match: {
PROCESSOR_ID: "1"
},
},
{
$group: {
_id: null,
totalCount: {
$sum: 1
},
priorityHighCount: {
$sum: {
$cond: [
{
$eq: [
"$ML_PRIORITY",
"HIGH"
]
},
1,
0
]
}
}
}
},
{
$project: {
EFFORTS: {
$round: {
"$multiply": [
{
$divide: [
"$priorityHighCount",
"$totalCount"
]
},
100
]
}
}
}
}
])