MongoDB equivalent of SELECT field AS `anothername`?

In MySQL, we give an alias name for a column. Similarly, you can give an alias name for field name in MongoDB using the $project stage in aggregation pipeline.

Syntax

db.collectionName.aggregate([
    { "$project": {
        "_id": 0,
        "aliasName": "$originalFieldName"
    }}
]);

Sample Data

Let us first create a collection with documents ?

db.selectFieldAsAnotherNameDemo.insertMany([
    {"Name": "Larry"},
    {"Name": "Robert"},
    {"Name": "Sam"},
    {"Name": "Mike"}
]);

{
    "acknowledged": true,
    "insertedIds": [
        ObjectId("5c9d448827b86948e204ca91"),
        ObjectId("5c9d449027b86948e204ca92"),
        ObjectId("5c9d449527b86948e204ca93"),
        ObjectId("5c9d449927b86948e204ca94")
    ]
}

Following is the query to display all documents from a collection with the help of find() method ?

db.selectFieldAsAnotherNameDemo.find().pretty();

{ "_id" : ObjectId("5c9d448827b86948e204ca91"), "Name" : "Larry" }
{ "_id" : ObjectId("5c9d449027b86948e204ca92"), "Name" : "Robert" }
{ "_id" : ObjectId("5c9d449527b86948e204ca93"), "Name" : "Sam" }
{ "_id" : ObjectId("5c9d449927b86948e204ca94"), "Name" : "Mike" }

Example

Following is the query for MongoDB equivalent of SELECT field AS `anothername` ?

db.selectFieldAsAnotherNameDemo.aggregate([
    { "$project": {
        "_id": 0,
        "StudentName": "$Name"
    }}
]);

{ "StudentName" : "Larry" }
{ "StudentName" : "Robert" }
{ "StudentName" : "Sam" }
{ "StudentName" : "Mike" }

Key Points

• Use $project stage in aggregation pipeline to create field aliases.
• Set "_id": 0 to exclude the ObjectId from output.
• Reference original field with "$fieldName" syntax.

Conclusion

MongoDB's $project stage provides field aliasing similar to SQL's AS clause. Use the aggregation pipeline to rename fields in query results with custom alias names.