//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'}})