Create Index in MongoDB

In MongoDB, indexes are created at the collection level, not on individual fields. Here's an example demonstrating how to create, drop, and manage indexes in MongoDB:

1. Creation of an index:

To create an index in MongoDB, you can use the createIndex() method. Let's say you have a collection named employees and you want to create an index on the employee_id field:

db.employees.createIndex({ employee_id: 1 });

This command creates an index on the employee_id field in ascending order (1).

2. Dropping an index:

To drop an existing index in MongoDB, you can use the dropIndex() method. For example, to drop the index on the employee_id field:

db.employees.dropIndex({ employee_id: 1 });

This command drops the index on the employee_id field.

3. Altering an existing index:

In MongoDB, you cannot directly alter an existing index. If you need to make changes to an existing index, you will need to drop the index and then recreate it with the desired changes.

4. Viewing existing indexes:

You can view existing indexes on a collection using the getIndexes() method:

db.employees.getIndexes();

This command will return information about all existing indexes on the employees collection.

In MongoDB, you do not alter a collection to add or remove indexes as you would in relational databases. Instead, indexes are managed directly at the collection level using methods like createIndex() and dropIndex().