Mongodb 建立索引

> db.person.ensureIndex({age:1});
{
"createdCollectionAutomatically" : false,
"numIndexesBefore" : 1,
"numIndexesAfter" : 2,
"ok" : 1
}

> db.person.ensureIndex({age:1},{unique:true});
{
"createdCollectionAutomatically" : false,
"numIndexesBefore" : 1,
"numIndexesAfter" : 2,
"ok" : 1
}

> db.person.dropIndex({age:1});
{ "nIndexesWas" : 2, "ok" : 1 }