{ _id: 5382dac91cb18bd025c2e522, username: '1', password: '1', __v: 0 },{ _id: 5383005d73410c901c2376a5, username: '2', password: '2', __v: 0 },{ _id: 5383006173410c901c2376a6, username: '3', password: '3', __v: 0 },{ _id: 5383007973410c901c2376a7, username: '测试', password: 'mima', __v: 0 }
请问我怎么查询出usename的字段集

db.collectionname.distinct(name)