Mongodb index

Create index
db.comment.createIndex({userid:1})
comment Is the name of the database , userid Is the field of the database

Look at the index
db.comment.getIndexes()

Create composite index
db.comment.createIndex({userid:1,nickname:-1})
Field names include userid and nickname

Remove index
db.comment.dropIndex({userid:1})
Remove complex indexes
db.comment.dropIndex("userid_1_nickname_-1")

Remove all of all
db.comment.dropIndexes()