index in mongodb code example

Example 1: mongodb index

db.collection.createIndex( { name: -1 } )

Example 2: compound index mongodb

db.collectionName.createIndex({field:value, field:value})


The order of fields listed in a compound index has significance. 
For instance, if a compound index consists of { userid: 1, score: -1 }, 
the index sorts first by userid and then, within each userid value, sorts by score.