Sparse Indexes in MongoDB
In MongoDB, it is not mandatory for all documents to contain the same fields.
Now, if you want to get all the documents in a MongoDB collection that contain only a specific field, then you may need to specify a common field as an index. This term is called a sparse index.
In this article, we will discuss sparse indexes in MongoDB . Also, we will provide a relevant example and explain it to make the topic easier to understand.
Sparse Indexes in MongoDB
The characteristic of sparse index is that it only contains documents with the specified index field, even if the value of the index field is empty. If any document does not have the index field, it will skip that document.
It is called a sparse index because the indexed field does not contain all the documents in the collection.
Creating a sparse index in a MongoDB collection
To create a sparse index in a MongoDB collection, we need to use the method createIndex(). The general format of this method is as follows:
db.Your_Collection.createIndex({ "Field": 1 }, { sparse: true })
In the following example command, we will create a sparse index containing the field Email in the collection mydata. The command will look like this:
db.mydata.createIndex({ "Email": 1 }, { sparse: true })
It is very important to understand that if you create a sparse index and query based on it, it may skip some documents in the collection.
请注意, the commands in this article are for MongoDB database and need to be run on the MongoDB console.
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