Indexes are used to find documents with specific field values quickly. Without an index, MySQL must begin with the first document and then read through the entire collection to find the relevant fields. The larger the collection, the more this costs. If a collection is large and queries on a specific field are common, then consider creating an index on a specific field inside a document.
For example, the following query will perform better with an index:
mysql-js> db.countryinfo.find("demographics.Population < 100") ...[output removed] 8 documents in set (0.00 sec)
createIndex() method creates an index
that you can define as nonunique or unique. Use the
field() method to chain the fields that
should be indexed. The
execute() method is
required to create or drop an index.
In MySQL, the
_id field is equivalent to a
primary key by default.
To create a nonunique index, pass to the
createIndex() method an index name.
Duplicate index names are prohibited.
In the following example, the first parameter of the
field() method specifies the Population
field inside the demographics object and the next parameter
indicates that the field should be indexed as an Integer
numeric value. The last parameter indicates whether the field
should require the NOT NULL constraint. If the value is
false, the field can contain
mysql-js> db.countryinfo.createIndex("pop"). field("demographics.Population", "INTEGER", false).execute() Query OK (0.04 sec)
To create a unique index, pass to the
createIndex() method an index name and the
mysqlx.IndexType.UNIQUE type. Country
"Name" is another common field in the
countryinfo collection to index. In the following example,
"Text(40)" represents the number of
characters to index and
true indicates that
the field cannot contain any
mysql-js> db.countryinfo.createIndex("name", mysqlx.IndexType.UNIQUE). field("Name", "TEXT(40)", true).execute() Query OK (0.04 sec)
To drop an index, pass to the
method the name of the index to drop. For example, you can
drop the “pop” index as follows:
mysql-js> db.countryinfo.dropIndex("pop").execute() Query OK (0.58 sec)
See Collection Index Management Functions for the full syntax definition.