Aggregate statistical calculations in MongoDB $SUM expression
- 2020-12-19 21:16:07
- OfStack
We usually calculate the sum through the expression $sum. Because MongoDB's documents have array fields, it is easy to divide the calculated sum into two categories:
1. Count the sum of a certain field of all documents that meet the conditions;
2. Count the sum of each data value in the array field of each document. Both cases can be done using the $sum expression.
The aggregate statistics of the above two cases correspond to those in the aggregate framework respectively
$group
Operation steps and
$project
Operating steps.
1.$group
So let's go straight to the example.
Case 1
The data in the test set mycol is as follows:
{
title: 'MongoDB Overview',
description: 'MongoDB is no sql database',
by_user: 'runoob.com',
url: 'http://www.runoob.com',
tags: ['mongodb', 'database', 'NoSQL'],
likes: 100
},
{
title: 'NoSQL Overview',
description: 'No sql database is very fast',
by_user: 'runoob.com',
url: 'http://www.runoob.com',
tags: ['mongodb', 'database', 'NoSQL'],
likes: 10
},
{
title: 'Neo4j Overview',
description: 'Neo4j is no sql database',
by_user: 'Neo4j',
url: 'http://www.neo4j.com',
tags: ['neo4j', 'database', 'NoSQL'],
likes: 750
}
Now let's calculate the number of articles written by each author using the above set, using aggregate()
db.mycol.aggregate([{$group : {_id : "$by_user", num_tutorial : {$sum : 1}}}])
The query results are as follows:
/* 1 */
{
"_id" : "Neo4j",
"num_tutorial" : 1
},
/* 2 */
{
"_id" : "runoob.com",
"num_tutorial" : 2
}
Case 2
Count the sum of each author by like, calculate the expression:
db.mycol.aggregate([{$group : {_id : "$by_user", num_tutorial : {$sum : "$likes"}}}])
The query results are as follows;
/* 1 */
{
"_id" : "Neo4j",
"num_tutorial" : 750
},
/* 2 */
{
"_id" : "runoob.com",
"num_tutorial" : 110
}
Case 3
The above example is a little simple. Let's enrich 1 more. The data of test set sales is as follows:
{ "_id" : 1, "item" : "abc", "price" : 10, "quantity" : 2, "date" : ISODate("2014-01-01T08:00:00Z") }
{ "_id" : 2, "item" : "jkl", "price" : 20, "quantity" : 1, "date" : ISODate("2014-02-03T09:00:00Z") }
{ "_id" : 3, "item" : "xyz", "price" : 5, "quantity" : 5, "date" : ISODate("2014-02-03T09:05:00Z") }
{ "_id" : 4, "item" : "abc", "price" : 10, "quantity" : 10, "date" : ISODate("2014-02-15T08:00:00Z") }
{ "_id" : 5, "item" : "xyz", "price" : 5, "quantity" : 10, "date" : ISODate("2014-02-15T09:05:00Z") }
The goal to be achieved is to group the daily sales based on the date, and the aggregate formula is as follows:
db.sales.aggregate(
[
{
$group:
{
_id: { day: { $dayOfYear: "$date"}, year: { $year: "$date" } },
totalAmount: { $sum: { $multiply: [ "$price", "$quantity" ] } },
count: { $sum: 1 }
}
}
]
)
The query results are:
{ "_id" : { "day" : 46, "year" : 2014 }, "totalAmount" : 150, "count" : 2 }
{ "_id" : { "day" : 34, "year" : 2014 }, "totalAmount" : 45, "count" : 2 }
{ "_id" : { "day" : 1, "year" : 2014 }, "totalAmount" : 20, "count" : 1 }
2. $project stage
Case 4
Suppose there is an students set, whose data structure is as follows:
{ "_id": 1, "quizzes": [ 10, 6, 7 ], "labs": [ 5, 8 ], "final": 80, "midterm": 75 }
{ "_id": 2, "quizzes": [ 9, 10 ], "labs": [ 8, 8 ], "final": 95, "midterm": 80 }
{ "_id": 3, "quizzes": [ 4, 5, 5 ], "labs": [ 6, 5 ], "final": 78, "midterm": 70 }
The current requirement is to calculate the sum of each student's ordinary test scores, experimental scores and final scores.
db.students.aggregate([
{
$project: {
quizTotal: { $sum: "$quizzes"},
labTotal: { $sum: "$labs" },
examTotal: { $sum: [ "$final", "$midterm" ] }
}
}
])
The query output results are as follows:
db.mycol.aggregate([{$group : {_id : "$by_user", num_tutorial : {$sum : 1}}}])
0
References:
https://www.runoob.com/mongodb/mongodb-aggregate.html
https://docs.mongodb.com/manual/reference/operator/aggregation/sum/index.html
conclusion