要练习查询首先要有数据，先用for循环插入了20条数据（就是javascript语法） >for(vari=1;i<=20;i++){db.student.insert({"name":"name"+
要练习查询首先要有数据，先用for循环插入了20条数据（就是javascript语法）
> for( var i=1;i<=20;i++){ db.student.insert({"name":"name"+i,"sort":"sort"+i,"tel":"1234"+i})}mongodb是用find来进行查询的，返回一个集合中文档的子集，子集合范围从0个文档到整个文档，也是通过参数决定要查询的细节。空的查询文档会匹配集合的所有内容，如要不指定查询内容，默认就是{}。
查询所有内容
语法：db.<集合名>.find()（类似于sql中的select * from 表名）【等同于db.<集合名>.find({})】
查询一条记录：
db.<集合名>.findOne();(findOne()首字母one要大写，~.~)
> db.student.findOne(){ "_id" : ObjectId("56e4d9e9bf48eabb5d350a99"), "name" : "name1", "sort" : "sort1", "tel" : "12341"}返回指定的键
语法：db.<集合>.find({}，{"键名":1,"键名":0})后面的这个{}里面指定要查询的内容，需要的就给参数 1，不需要的就给参数0（类似于sql中select 列名，列名 from 表名）
> db.student.find({},{name:1,_id:0}){ "name" : "name1" }{ "name" : "name2" }{ "name" : "name3" }{ "name" : "name4" }{ "name" : "name5" }{ "name" : "name6" }{ "name" : "name7" }{ "name" : "name8" }{ "name" : "name9" }{ "name" : "name10" }{ "name" : "name11" }{ "name" : "name12" }{ "name" : "name13" }{ "name" : "name14" }{ "name" : "name15" }{ "name" : "name16" }{ "name" : "name17" }{ "name" : "name18" }{ "name" : "name19" }{ "name" : "name20" }只要name这个键，默认的会返回_id,我们设置_id:0即可。
查询条件
在第一个{}来指定条件，进行查询，类似sql中的where查询
> db.student.find({"tel":{"$gte":"123410","$lte":"123413"}}){ "_id" : ObjectId("56e4d9e9bf48eabb5d350aa2"), "name" : "name10", "sort" : "sort10", "tel" : "123410" }{ "_id" : ObjectId("56e4d9e9bf48eabb5d350aa3"), "name" : "name11", "sort" : "sort11", "tel" : "123411" }{ "_id" : ObjectId("56e4d9e9bf48eabb5d350aa4"), "name" : "name12", "sort" : "sort12", "tel" : "123412" }{ "_id" : ObjectId("56e4d9e9bf48eabb5d350aa5"), "name" : "name13", "sort" : "sort13", "tel" : "123413" }查询tel在123410和123413之间的文档。
下面这个是指定记录查询，有点类似于sql中的(select * from student where tel="12342";)
> db.student.find({"tel":"12342"}){ "_id" : ObjectId("56e4d9e9bf48eabb5d350a9a"), "name" : "name2", "sort" : "sort2", "tel" : "12342" }> db.student.find({"tel":"12342","name":"123"})> db.student.find({"tel":"12342","name":"name2"}){ "_id" : ObjectId("56e4d9e9bf48eabb5d350a9a"), "name" : "name2", "sort" : "sort2", "tel" : "12342" }在find前面一个{}里面用,连接的映射条件，其实就是and条件的查询，
在mongodb中也有对应的 or 查询使用的,符号是 $or
> db.student.find({$or:[{"name":"name2"},{"name":"name3"}]}){ "_id" : ObjectId("56e4d9e9bf48eabb5d350a9a"), "name" : "name2", "sort" : "sort2", "tel" : "12342" }{ "_id" : ObjectId("56e4d9e9bf48eabb5d350a9b"), "name" : "name3", "sort" : "sort3", "tel" : "12343" }$in基本上也是or的关系，和MySQL中的in(..,..,...)类似 另外$nin和$in关系是相反的，类似于 not in(,)
> db.student.find({"tel":{$in:["12341","12342","123420"]}}){ "_id" : ObjectId("56e4d9e9bf48eabb5d350a99"), "name" : "name1", "sort" : "sort1", "tel" : "12341" }{ "_id" : ObjectId("56e4d9e9bf48eabb5d350a9a"), "name" : "name2", "sort" : "sort2", "tel" : "12342" }{ "_id" : ObjectId("56e4d9e9bf48eabb5d350aac"), "name" : "name20", "sort" : "sort20", "tel" : "123420" }$all用来通过多个元素匹配数组数组
> db.food.insert({"animal":["dog","cat","python"]})> db.food.insert({"animal":["dog","cat","pig"]})> db.food.insert({"animal":["pig","cat","python"]})> db.food.find({"animal":{$all:["cat","python"]}},{_id:0}){ "animal" : [ "dog", "cat", "python" ] }{ "animal" : [ "pig", "cat", "python" ] }排序.sort
语法：db.<集合名>.find().sort({"键名":1})（参数1为升序，-1为降序）
限制数目 .limit
语法：db.<集合名>.find().limit(number)(number为限制返回的数目)
> db.student.find().sort({"tel":1}).limit(5){ "_id" : ObjectId("56e4d9e9bf48eabb5d350a99"), "name" : "name1", "sort" : "sort1", "tel" : "12341" }{ "_id" : ObjectId("56e4d9e9bf48eabb5d350aa2"), "name" : "name10", "sort" : "sort10", "tel" : "123410" }{ "_id" : ObjectId("56e4d9e9bf48eabb5d350aa3"), "name" : "name11", "sort" : "sort11", "tel" : "123411" }{ "_id" : ObjectId("56e4d9e9bf48eabb5d350aa4"), "name" : "name12", "sort" : "sort12", "tel" : "123412" }{ "_id" : ObjectId("56e4d9e9bf48eabb5d350aa5"), "name" : "name13", "sort" : "sort13", "tel" : "123413" }> db.student.find().sort({"tel":-1}).limit(5){ "_id" : ObjectId("56e4d9e9bf48eabb5d350aa1"), "name" : "name9", "sort" : "sort9", "tel" : "12349" }{ "_id" : ObjectId("56e4d9e9bf48eabb5d350aa0"), "name" : "name8", "sort" : "sort8", "tel" : "12348" }{ "_id" : ObjectId("56e4d9e9bf48eabb5d350a9f"), "name" : "name7", "sort" : "sort7", "tel" : "12347" }{ "_id" : ObjectId("56e4d9e9bf48eabb5d350a9e"), "name" : "name6", "sort" : "sort6", "tel" : "12346" }{ "_id" : ObjectId("56e4d9e9bf48eabb5d350a9d"), "name" : "name5", "sort" : "sort5", "tel" : "12345" }上面是对tel进行降序和升序的查询。并指定返回5条记录
跳过记录：.skip(number)
> db.student.find().skip(15){ "_id" : ObjectId("56e4d9e9bf48eabb5d350aa8"), "name" : "name16", "sort" : "sort16", "tel" : "123416" }{ "_id" : ObjectId("56e4d9e9bf48eabb5d350aa9"), "name" : "name17", "sort" : "sort17", "tel" : "123417" }{ "_id" : ObjectId("56e4d9e9bf48eabb5d350aaa"), "name" : "name18", "sort" : "sort18", "tel" : "123418" }{ "_id" : ObjectId("56e4d9e9bf48eabb5d350aab"), "name" : "name19", "sort" : "sort19", "tel" : "123419" }{ "_id" : ObjectId("56e4d9e9bf48eabb5d350aac"), "name" : "name20", "sort" : "sort20", "tel" : "123420" }一共20行记录，省略了前面15行，只返回后面5行
可以使用.skip().limit()实现翻页的功能
> db.student.find().skip(5).limit(5){ "_id" : ObjectId("56e4d9e9bf48eabb5d350a9e"), "name" : "name6", "sort" : "sort6", "tel" : "12346" }{ "_id" : ObjectId("56e4d9e9bf48eabb5d350a9f"), "name" : "name7", "sort" : "sort7", "tel" : "12347" }{ "_id" : ObjectId("56e4d9e9bf48eabb5d350aa0"), "name" : "name8", "sort" : "sort8", "tel" : "12348" }{ "_id" : ObjectId("56e4d9e9bf48eabb5d350aa1"), "name" : "name9", "sort" : "sort9", "tel" : "12349" }{ "_id" : ObjectId("56e4d9e9bf48eabb5d350aa2"), "name" : "name10", "sort" : "sort10", "tel" : "123410" }> db.student.find().skip(10).limit(5){ "_id" : ObjectId("56e4d9e9bf48eabb5d350aa3"), "name" : "name11", "sort" : "sort11", "tel" : "123411" }{ "_id" : ObjectId("56e4d9e9bf48eabb5d350aa4"), "name" : "name12", "sort" : "sort12", "tel" : "123412" }{ "_id" : ObjectId("56e4d9e9bf48eabb5d350aa5"), "name" : "name13", "sort" : "sort13", "tel" : "123413" }{ "_id" : ObjectId("56e4d9e9bf48eabb5d350aa6"), "name" : "name14", "sort" : "sort14", "tel" : "123414" }{ "_id" : ObjectId("56e4d9e9bf48eabb5d350aa7"), "name" : "name15", "sort" : "sort15", "tel" : "123415" }聚合操作
求数目
语法：db.<集合>.count() ；类似于sql中select count(*) from 表名
> db.student.count()20> db.student.find().limit(1){ "_id" : ObjectId("56e4d9e9bf48eabb5d350a99"), "name" : "name1", "sort" : "sort1", "tel" : "12341" }如果是求某一列的
> db.student.count({},{"name":1})20一般的数学运算
先模拟数据
> for(var i=1;i<20;i++){db.test1.insert({"num":i})}WriteResult({ "nInserted" : 1 })下面是关于一列的求和，最大值，最小值，和平均值
语法：db.<集合名>.aggregate({$group:{_id:" ",返回的名字:{函数:"$列名"}}})
> db.test1.aggregate({$group:{_id:" ",sumsal:{$sum:"$num"}}}){ "_id" : " ", "sumsal" : 190 }> db.test1.aggregate({$group:{_id:" ",sumsal:{$max:"$num"}}}){ "_id" : " ", "sumsal" : 19 }> db.test1.aggregate({$group:{_id:" ",sumsal:{$min:"$num"}}}){ "_id" : " ", "sumsal" : 1 }> db.test1.aggregate({$group:{_id:" ",sumsal:{$avg:"$num"}}}){ "_id" : " ", "sumsal" : 10 }在mangodb中进行sql中group by 的操作，只需要在原来基础空格上加上列名
重新模拟数据
> for(var i=1;i<5;i++){db.test2.insert({"num":i,"type":1})}WriteResult({ "nInserted" : 1 })> for(var i=5;i<10;i++){db.test2.insert({"num":i,"type":2})}WriteResult({ "nInserted" : 1 })> for(var i=10;i<15;i++){db.test2.insert({"num":i,"type":3})}WriteResult({ "nInserted" : 1 })> db.test2.aggregate({$group:{_id:"$type",sumsal:{$avg:"$num"}}}){ "_id" : 3, "sumsal" : 12 }{ "_id" : 2, "sumsal" : 7 }{ "_id" : 1, "sumsal" : 2.5 }如果需要组名
> db.test2.aggregate({$group:{_id:{type:"$type"},sumsal:{$sum:"$num"}}}){ "_id" : { "type" : 3 }, "sumsal" : 60 }{ "_id" : { "type" : 2 }, "sumsal" : 35 }{ "_id" : { "type" : 1 }, "sumsal" : 10 }多列分组，在原来的基础上在进行分组
固定的字符串，我们只需要定义列名就行咯
> db.test2.aggregate({$group:{_id:{type:"$type","名字":"列名"},sumsal:{$sum:"$num"}}})