Description
MongoDB Aggregation functions execute informational records and rebounds the expected output. In MongoDB Aggregation operations are used where as in sql database count functions are performed. The functions of aggregation are an association of key esteems among different records that are well balanced, and execute an assortment of activities that associates the information to give back a solitary output.
Syntax
The syntax for MongoDB Aggregation functions is as follows:
>db.collection_name.aggregate(aggregate_operation)
Aggregate operation =>Process the required records.
Description
The following are the aggregate operation in mongodb database.
| Function | Explanation | Example |
|---|---|---|
| $sum | sum up the characterised esteem from all the records from the set. | db.mycol.aggregate([{$group:{_id:"$by_user",num_tutorials:{$sum:"$likes"}}}]) |
| $min | Retrieves the minimum esteem in the corresponding records. | db.mycol.aggregate([{$group:{_id:"$by_user",num_tutorial:{$min:"$like"}}}]) |
| $avg | Ascertains the normal of every given quality from all reports in the gathering. | db.mycol.aggregate([{$group:{_id:"$by_user",num_tutorial:{$avg:"$like"}}}]) |
| $max | Retrieves the maximum esteem in the corresponding records. | db.mycol.aggregate([{$group:{_id:"$by_user",num_tutorial:{$max:"$likes"}}}]) |
| $last | Retrives the last record from the main record set | db.mycol.aggregate([{$group:{_id:"$by_user",last_url:{$last:"$url"}}}]) |
| $first | Retrives the first record from the corresponding record set | db.mycol.aggregate([{$group:{_id:"$by_user",first_url:{$first:"$url"}}}]) |
| $addToset | Inserting the esteems inside the array | db.mycol.aggregate([{$group:{_id:"$by_user",first_url:{$first:"$url"}}}]) |
| $push | Inserting the esteems inside the array from the output records | db.mycol.aggregate([{$group:{_id:"$by_user",url:{$addToset:"$url"}}}]) |
Examples
By viewing the below example,the concept of MongoDB Aggregation operations can be easily understand.
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MongoDB shell version:2.6.1
connecting to: test
use school
switched to db school
>db.students.find();
{"_id":objectId("56c63217089b3c7e483bd97"),"StudentNo": "1","FirstName":"Mark","LastName":"Masen","Gender":"Male","Age":"14"}
{"_id":objectId("56c63217089b3c7e483bd98"),"StudentNo": "2","FirstName":"Mel","LastName":"Gibson","Gender":"Female","Age":"17"}
{"_id":objectId("56c63217089b3c7e483bd99"),"StudentNo": "3","FirstName":"Deno","LastName":"Socratus","Gender":"Male","Age":"40"}
{"_id":objectId("56c63217089b3c7e483bd9a"),"StudentNo": "4","FirstName":"Shay","LastName":"Whatson","Gender":"Female","Age":"32"}
>db.students.aggregate([{$group:{_id:"$Gender",MyResult:{$sum:1}}}]);
{"_id":"Male","MyResult":3}
{"_id":"Female","MyResult":3}
>db.students.aggregate([{$group:{_id:"$Gender",MaxAge:{$max:"Age"}}}]);
{"_id":"Male","MaxAge":"Age"}
{"_id":"Female","MaxAge":"Age"}
>db.students.aggregate([{$group:{_id:"$Gender",MaxAge:{$max:"Age"}}}]);
{"_id":"Male","MaxAge":"40"}
{"_id":"Female","MaxAge":"32"}
>db.students.aggregate([{$group:{_id:"$Gender",MinAge:{$min:"Age"}}}]);
{"_id":"Male","MinAge":"14"}
{"_id":"Female","MinAge":"17"}
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Here in the above example the concept of MongoDB Aggregation operations are defined such as maximum and minimum functional operations.
Key Points
- MongoDB Aggregations - Are the functions that execute informational records and rebounds the desire output.
- Aggregate functions- Aggregate functions are $sum, $min, $max, $avg, $last, $first, $addToset, $push.