MongoDB Aggregation Pipeline (aggregate)

1. Aggregation function

• Total number of queries. COUNT ()

>Db.userinfo.count ()3> Db.userinfo.Find(){ "_id":1,"name":"Uncle Guo","Sex":"male"," Age":" the" }{ "_id":2,"name":"Miss Guo","Sex":"male"," Age":"Unknown" }{ "_id":3,"name":"Master Guo","Sex":"male"," Age":" -"}

2. Aggregate () method

Let's insert some test data first.

{     "_id": ObjectId ("5abc960c684781cda6d38027"),     "Name": "Uncle Guo",     "Sex": "Male",     "Age": 80.0,     "Skil" : [        "PHP",         "Js",         "MYSQL",         "Html",         "Css"    ]}{     "_id": ObjectId ("5abc960c684781cda6d38028"),     "Name": "Uncle Guo",     "Sex": "Male",     "Age": 60.0,     "Skil" : [        "PHP",         "MYSQL"    ]}{     "_id": ObjectId ("5abc960c684781cda6d38029"),     "Sex": "Female"}{     "_id": ObjectId ("5abc960c684781cda6d3802a"),     "Name": "Master Guo",     "Sex": "Male",     "Age": 18.0,     "Skil" : [        "Css",         "Java",         "Html"    ]}

• Sum

Check the sum of all ages

db.userinfo.aggregate ([    {$group: {        null,        ' $age '}}    }])

Results

{     null,     "age_sum": 158.0}

• Average
• Minimum value
• Maximum Value
• Get the first document
• Get the last document

MongoDB Aggregation Pipeline (aggregate)