How can I count distinct values in MongoDB?

MongoDB has a distinct command which returns an array of distinct values for a field; you can check the length of the array for a count. As noted in the MongoDB documentation: Results must not be larger than the maximum BSON size (16MB).

What does distinct do in MongoDB?

distinct() considers each element of the array as a separate value. For instance, if a field has as its value [ 1, [1], 1 ] , then db. collection. distinct() considers 1 , [1] , and 1 as separate values.

How do I count documents in MongoDB?

Returns the count of documents that would match a find() query for the collection or view. The db. collection. count() method does not perform the find() operation but instead counts and returns the number of results that match a query.

How do I set unique fields in MongoDB?

To create a unique index, use the db. collection. createIndex() method with the unique option set to true .

How do I edit an index in MongoDB?

To modify an existing index in MongoDB Compass, you need to drop and recreate the index. See also: MongoDB Compass Documentation.

Which method calculates aggregate values for the data in a collection or a view?

collection.aggregate() method
collection. aggregate() method is used to calculate aggregate values for the data in a collection. A sequence of data aggregation operations or stages.

How do I remove duplicates in MongoDB?

Query the duplicate row using findOne() method and store it as an object.

1. const User = db. User. findOne({_id:”duplicateid”}); 2.Execute deleteMany() method to remove all the rows with the id “duplicateid”
2. db. User. deleteMany({_id:”duplicateid”}); Insert the values stored in User object.
3. db. User. insertOne(User);

What is a unique index?

Unique indexes are indexes that help maintain data integrity by ensuring that no rows of data in a table have identical key values. When you create a unique index for an existing table with data, values in the columns or expressions that comprise the index key are checked for uniqueness.

How to group by and count with MongoDB?

What is an aggregation operation?

What is query in MongoDB?

– Field selection. – Finding a single document. – Displaying documents in a formatted way. – Equal filter query. – Check the existence filter query. – Logical operator query – Project query. – Limit Query.

What does collection mean in MongoDB?

MongoDB stores data in the form of documents, which are stored in collections, while collections are stored in the database. A collection can store a number of documents that might not be the same in structure. Since MongoDB is a Schema-free DB, a collection can store documents with varying structures.

How to query MongoDB with SQL SELECT?

– The find method call on the customers collection maps to the SELECT statement’s FROM clause. – The find statement’s query section maps to the SELECT statement’s WHERE clause. – The find statement’s projection section maps to the SELECT statement’s SELECT clause. – The find statement’s sort section maps to the SELECT statement’s ORDER BY clause.