1、使用比较运算符查询

MongoDB	运算
$gt	大于
$lt	小于
$gte	大于等于
$lte	小于等于欧
$ne	不等于

db.集合名.find({"键名": {比较运算符1:值1, 比较运算符2:值2} })

> db.students.find()
{ "_id" : ObjectId("5db642b30f98841018f76965"), "name" : "chen", "age" : 18, "grade" : "一年级" }
{ "_id" : ObjectId("5db642bc0f98841018f76966"), "name" : "wang", "age" : 19, "grade" : "二年级" }
{ "_id" : ObjectId("5db653920f98841018f7696b"), "name" : "xu", "age" : 20, "grade" : "三年级" }
{ "_id" : ObjectId("5db654660f98841018f7696c"), "name" : "ma", "age" : 20, "grade" : "二年级" }
> db.students.find({"age": {$lt:19}})
{ "_id" : ObjectId("5db642b30f98841018f76965"), "name" : "chen", "age" : 18, "grade" : "一年级" }
> db.students.find({"age": {$gte:18,$lt:20}})
{ "_id" : ObjectId("5db642b30f98841018f76965"), "name" : "chen", "age" : 18, "grade" : "一年级" }
{ "_id" : ObjectId("5db642bc0f98841018f76966"), "name" : "wang", "age" : 19, "grade" : "二年级" }

2、使用关键字查询

2.1、in/not in 关键字

db.集合名.find({"键名": {$in:[值1, 值2, 值3 ...]} })
db.集合名.find({"键名": {$nin:[值1, 值2, 值3 ...]} })

> db.students.find({"age":{$in:[19,18,17]}})
{ "_id" : ObjectId("5db642b30f98841018f76965"), "name" : "chen", "age" : 18, "grade" : "一年级" }
{ "_id" : ObjectId("5db642bc0f98841018f76966"), "name" : "wang", "age" : 19, "grade" : "二年级" }
> db.students.find({"age":{$nin:[19,18,17]}})
{ "_id" : ObjectId("5db653920f98841018f7696b"), "name" : "xu", "age" : 20, "grade" : "三年级" }
{ "_id" : ObjectId("5db654660f98841018f7696c"), "name" : "ma", "age" : 20, "grade" : "二年级" }

2.2、size 关键字

对于值为list的字段，可以对list的长度(即list当中值的个数)进行判断来查询。

db.集合名.find({"键名": {$size:n} })

> db.students.find()
{ "_id" : ObjectId("5db642b30f98841018f76965"), "name" : "chen", "age" : 18, "grade" : "一年级" }
{ "_id" : ObjectId("5db642bc0f98841018f76966"), "name" : "wang", "age" : 19, "grade" : "二年级" }
{ "_id" : ObjectId("5db653920f98841018f7696b"), "name" : "xu", "age" : 20, "grade" : "三年级", "text" : [ "女", "研究员" ] }
{ "_id" : ObjectId("5db654660f98841018f7696c"), "name" : "ma", "age" : 20, "grade" : "二年级", "text" : [ "女", "副教授", "副处长" ] }
# 查找text字段长度为3的数据
> db.students.find({"text":{$size:3}})
{ "_id" : ObjectId("5db654660f98841018f7696c"), "name" : "ma", "age" : 20, "grade" : "二年级", "text" : [ "女", "副教授", "副处长" ] }

2.3、exists 关键字

查询包含/不包含某个字段的数据

db.集合名.find({"键名": {$exist: true|fase} })   # t、f要小写

> db.students.find()
{ "_id" : ObjectId("5db642b30f98841018f76965"), "name" : "chen", "age" : 18, "grade" : "一年级" }
{ "_id" : ObjectId("5db642bc0f98841018f76966"), "name" : "wang", "age" : 19, "grade" : "二年级" }
{ "_id" : ObjectId("5db653920f98841018f7696b"), "name" : "xu", "age" : 20, "grade" : "三年级", "text" : [ "女", "研究员" ] }
{ "_id" : ObjectId("5db654660f98841018f7696c"), "name" : "ma", "age" : 20, "grade" : "二年级", "text" : [ "女", "副教授", "副处长" ] }
# 查询包含text字段的数据
> db.students.find({"text":{$exists:true}})
{ "_id" : ObjectId("5db653920f98841018f7696b"), "name" : "xu", "age" : 20, "grade" : "三年级", "text" : [ "女", "研究员" ] }
{ "_id" : ObjectId("5db654660f98841018f7696c"), "name" : "ma", "age" : 20, "grade" : "二年级", "text" : [ "女", "副教授", "副处长" ] }
# 查询不含text字段的数据
> db.students.find({"text":{$exists:false}})
{ "_id" : ObjectId("5db642b30f98841018f76965"), "name" : "chen", "age" : 18, "grade" : "一年级" }
{ "_id" : ObjectId("5db642bc0f98841018f76966"), "name" : "wang", "age" : 19, "grade" : "二年级" }

2.4、or 关键字

db.集合名.find({$or:[{条件1}, {条件2}, {条件3}...]})

> db.students.find()
{ "_id" : ObjectId("5db642b30f98841018f76965"), "name" : "chen", "age" : 18, "grade" : "一年级" }
{ "_id" : ObjectId("5db642bc0f98841018f76966"), "name" : "wang", "age" : 19, "grade" : "二年级" }
{ "_id" : ObjectId("5db653920f98841018f7696b"), "name" : "xu", "age" : 20, "grade" : "三年级", "text" : [ "女", "研究员" ] }
{ "_id" : ObjectId("5db654660f98841018f7696c"), "name" : "ma", "age" : 20, "grade" : "二年级", "text" : [ "女", "副教授", "副处长" ] }
# 查询包含text字段或者name=chen的数据
> db.students.find({$or:[{"text":{$exists:true}},{"name":"chen"}]})
{ "_id" : ObjectId("5db642b30f98841018f76965"), "name" : "chen", "age" : 18, "grade" : "一年级" }
{ "_id" : ObjectId("5db653920f98841018f7696b"), "name" : "xu", "age" : 20, "grade" : "三年级", "text" : [ "女", "研究员" ] }
{ "_id" : ObjectId("5db654660f98841018f7696c"), "name" : "ma", "age" : 20, "grade" : "二年级", "text" : [ "女", "副教授", "副处长" ] }

3、模糊查询

db.集合名.find({"键名": js正则表达)

> db.students.find()
{ "_id" : ObjectId("5db642b30f98841018f76965"), "name" : "chen", "age" : 18, "grade" : "一年级" }
{ "_id" : ObjectId("5db642bc0f98841018f76966"), "name" : "wang", "age" : 19, "grade" : "二年级" }
{ "_id" : ObjectId("5db653920f98841018f7696b"), "name" : "xu", "age" : 20, "grade" : "三年级", "text" : [ "女", "研究员" ] }
{ "_id" : ObjectId("5db654660f98841018f7696c"), "name" : "ma", "age" : 20, "grade" : "二年级", "text" : [ "女", "副教授", "副处长" ] }
{ "_id" : ObjectId("5db68d190f98841018f76970"), "name" : "cheng", "age" : 21, "grade" : "四年级" }
# 查询name以che开头的数据
> db.students.find({"name":/che/})
{ "_id" : ObjectId("5db642b30f98841018f76965"), "name" : "chen", "age" : 18, "grade" : "一年级" }
{ "_id" : ObjectId("5db68d190f98841018f76970"), "name" : "cheng", "age" : 21, "grade" : "四年级" }

4、查询结果排序

db.集合名.find().sort({"键名": 1｜-1, "键名": 1｜-1...})
 1 为升序  
-1 为降序

> db.students.find().sort({"name":1, "age":-1})
{ "_id" : ObjectId("5db642b30f98841018f76965"), "name" : "chen", "age" : 18, "grade" : "一年级" }
{ "_id" : ObjectId("5db68f6c0f98841018f76971"), "name" : "cheng", "age" : 22, "grade" : "五年级" }
{ "_id" : ObjectId("5db68d190f98841018f76970"), "name" : "cheng", "age" : 21, "grade" : "四年级" }
{ "_id" : ObjectId("5db654660f98841018f7696c"), "name" : "ma", "age" : 20, "grade" : "二年级", "text" : [ "女", "副教授", "副处长" ] }
{ "_id" : ObjectId("5db642bc0f98841018f76966"), "name" : "wang", "age" : 19, "grade" : "二年级" }
{ "_id" : ObjectId("5db653920f98841018f7696b"), "name" : "xu", "age" : 20, "grade" : "三年级", "text" : [ "女", "研究员" ] }

5、限定返回结果数量

db.集合名.find().limit(n)
db.集合名.find().skip(n)  # 跳过n条，返回从n+1k开始的数据
db.集合名.find().skip(n).limit(m)  # 跳过n条，返回后面的m条

.limit() 与 .sort()无先后顺序

# 按age正序排列，并返回前两行数据
> db.students.find().limit(2).sort({"age":1})
{ "_id" : ObjectId("5db642b30f98841018f76965"), "name" : "chen", "age" : 18, "grade" : "一年级" }
{ "_id" : ObjectId("5db642bc0f98841018f76966"), "name" : "wang", "age" : 19, "grade" : "二年级" }
> db.students.find().sort({"age":1}).limit(2)
{ "_id" : ObjectId("5db642b30f98841018f76965"), "name" : "chen", "age" : 18, "grade" : "一年级" }
{ "_id" : ObjectId("5db642bc0f98841018f76966"), "name" : "wang", "age" : 19, "grade" : "二年级" }
# 查询age第二小和第三小的数据
> db.students.find().skip(1).limit(2).sort({"age":1})
{ "_id" : ObjectId("5db642bc0f98841018f76966"), "name" : "wang", "age" : 19, "grade" : "二年级" }
{ "_id" : ObjectId("5db653920f98841018f7696b"), "name" : "xu", "age" : 20, "grade" : "三年级", "text" : [ "女", "研究员" ] }

6、查询返回结果数量

db.集合名.find().count()
db.集合名.find().skip(n).count(true)  # 与skip结合使用时，要加true

> db.students.find({"name":"cheng"}).count()
2

> db.students.find().count()
6
# 不加true就会统计全部数据条目
> db.students.find().skip(2).count()    
6
> db.students.find().skip(2).count(true)
4

7、创建索引

db.集合名.ensureIndex({"键名1":1|-1, "键名2":1|-1})

> db.students.ensureIndex({"name":1})
{
    "createdCollectionAutomatically" : false,
    "numIndexesBefore" : 1,
    "numIndexesAfter" : 2,
    "ok" : 1
}