Concept of Index in MongoDB

  • Indexes support the efficient execution of queries in MongoDB.
  • Without indexes, MongoDB must perform a collection scan, i.e. scan every document in a collection, to select those documents that match the query statement.
  • It is one of way to create unique constraints similar to SQL Unique Constraints.
  • The index stores the value of a specific field or set of fields, ordered by the value of the field. The ordering of the index entries supports efficient equality matches and range-based query operations.
  • Indexes in MongoDB are similar to indexes in other database systems.
NOTE:-
  1. MongoDB creates a unique index on the _id field during the creation of a collection.
  2. The _id index prevents clients from inserting two documents with the same value for the _id field.
  3. You cannot drop this index on the _id field.