//字段操作服符
db.person.remove() db.person.insert([ {name:'zs', age:17, gender:'男'}, {name:'ls', age:18}, {name:'ww', age:19}, {name:'it666', age:20, gender:'女'} ]) //需求:要求查询出所有拥有gender属性的文档: db.person.find({gender:{$exists:true}}) //查询出所有男性: //应用场景:配合$ne/$nor/$not来清理数据 db.person.find({gender:{$ne:'男'}}) //查询出不是男且字段不为空的人: db.person.find({gender:{$ne:'男',$exists:true}}) db.person.insert([ {name:'itzb', age:'88'}, {name:'lnj', age:'999'} ]) db.person.find() //查出所有年龄为字符串的文档 db.person.find({age:{$type:'string'}})