查询
MongoDB为我们提供了很强大的查询功能，之前演示的都比较简单，接下来将展示一些进阶用法。
数据准备
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| db.personalinfo.remove({});
db.personalinfo.save({name:'zhangsan',age:10});
db.personalinfo.save({name:'lisi',age:11});
db.personalinfo.save({name:'wangsu',age:12});
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根据某个字段查询
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| > db.personalinfo.find({age:11});
{ "_id" : ObjectId("5a498d86f0ec47e9f5ce2db5"), "name" : "lisi", "age" : 11 }
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过滤返回的字段
find的第二个参数可以设置需要返回的字段，以节省网络传输
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| > db.personalinfo.find({}, {name:1});
{ "_id" : ObjectId("5a498d86f0ec47e9f5ce2db4"), "name" : "zhangsan" }
{ "_id" : ObjectId("5a498d86f0ec47e9f5ce2db5"), "name" : "lisi" }
{ "_id" : ObjectId("5a498d87f0ec47e9f5ce2db6"), "name" : "wangsu" }
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不能同时使用包含或者排除，如果需要排除，直接不写age的字段即可。
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| > db.personalinfo.find({}, {name:1, age:0});
Error: error: {
"ok" : 0,
"errmsg" : "Projection cannot have a mix of inclusion and exclusion.",
"code" : 2,
"codeName" : "BadValue"
}
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findOne()
findOne()跟find()的参数是一样的，只是findOne只返回查询到的第一条数据。
条件运算符
大于&小于
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| > db.personalinfo.find({age:{$gt:10}});
{ "_id" : ObjectId("5a498d86f0ec47e9f5ce2db5"), "name" : "lisi", "age" : 11 }
{ "_id" : ObjectId("5a498d87f0ec47e9f5ce2db6"), "name" : "wangsu", "age" : 12 }
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- 大于：$gt
- 大于等于：$gte
- 小于：$lt
- 小于等于：$lte
多个条件：
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| > db.personalinfo.find({age:{$gt:10,$lt:12}});
{ "_id" : ObjectId("5a498d86f0ec47e9f5ce2db5"), "name" : "lisi", "age" : 11 }
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$all
$all运算符表示从数组中过滤包含的字段
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| db.address.insert({name:['beijing','tianjin']});
db.address.insert({name:['beijing','shanghai']});
db.address.insert({name:['dalian','shanghai']});
> db.address.find({name: {$all: ['beijing','tianjin']}});
{ "_id" : ObjectId("5a4994c2f0ec47e9f5ce2db7"), "name" : [ "beijing", "tianjin" ] }
> db.address.find({name: {$all: ['shanghai']}});
{ "_id" : ObjectId("5a4994c2f0ec47e9f5ce2db8"), "name" : [ "beijing", "shanghai" ] }
{ "_id" : ObjectId("5a4994c2f0ec47e9f5ce2db9"), "name" : [ "dalian", "shanghai" ] }
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$exists
查询包含某个字段的文档。
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| > db.personalinfo.find({age:{$exists:true}});
{ "_id" : ObjectId("5a498d86f0ec47e9f5ce2db4"), "name" : "zhangsan", "age" : 10 }
{ "_id" : ObjectId("5a498d86f0ec47e9f5ce2db5"), "name" : "lisi", "age" : 11 }
{ "_id" : ObjectId("5a498d87f0ec47e9f5ce2db6"), "name" : "wangsu", "age" : 12 }
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$exists要和$in结合使用来判断某个字段的值为null，并且字段真的存在的情况下，默认age:null的查询方式，会把没有这个字段的数据也查出来。
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| > db.personalinfo.insert({name:'zhaoliu', age:null});
WriteResult({ "nInserted" : 1 })
> db.personalinfo.insert({name:'zhaoliu', myage:14});
WriteResult({ "nInserted" : 1 })
> db.personalinfo.find({age:null});
{ "_id" : ObjectId("5a499774f0ec47e9f5ce2dba"), "name" : "zhaoliu", "age" : null }
{ "_id" : ObjectId("5a49977ef0ec47e9f5ce2dbb"), "name" : "zhaoliu", "myage" : 14 }
> db.personalinfo.find({age:{$in:[null],$exists: true}});
{ "_id" : ObjectId("5a499774f0ec47e9f5ce2dba"), "name" : "zhaoliu", "age" : null }
>
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$mod
$mod是取模
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| > db.personalinfo.find({age:{$mod:[5,2]}});
{ "_id" : ObjectId("5a498d87f0ec47e9f5ce2db6"), "name" : "wangsu", "age" : 12 }
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$ne
$ne表示不等于
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| > db.personalinfo.find({age:{$ne:5}});
{ "_id" : ObjectId("5a498d86f0ec47e9f5ce2db4"), "name" : "zhangsan", "age" : 10 }
{ "_id" : ObjectId("5a498d86f0ec47e9f5ce2db5"), "name" : "lisi", "age" : 11 }
{ "_id" : ObjectId("5a498d87f0ec47e9f5ce2db6"), "name" : "wangsu", "age" : 12 }
{ "_id" : ObjectId("5a499774f0ec47e9f5ce2dba"), "name" : "zhaoliu", "age" : null }
{ "_id" : ObjectId("5a49977ef0ec47e9f5ce2dbb"), "name" : "zhaoliu", "myage" : 14 }
> db.personalinfo.find({age:{$ne:5, $exists:1}});
{ "_id" : ObjectId("5a498d86f0ec47e9f5ce2db4"), "name" : "zhangsan", "age" : 10 }
{ "_id" : ObjectId("5a498d86f0ec47e9f5ce2db5"), "name" : "lisi", "age" : 11 }
{ "_id" : ObjectId("5a498d87f0ec47e9f5ce2db6"), "name" : "wangsu", "age" : 12 }
{ "_id" : ObjectId("5a499774f0ec47e9f5ce2dba"), "name" : "zhaoliu", "age" : null }
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$in
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| > db.personalinfo.find({age:{$in:[11,12]}});
{ "_id" : ObjectId("5a498d86f0ec47e9f5ce2db5"), "name" : "lisi", "age" : 11 }
{ "_id" : ObjectId("5a498d87f0ec47e9f5ce2db6"), "name" : "wangsu", "age" : 12 }
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not in
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| > db.personalinfo.find({age:{$nin:[11,12]}});
{ "_id" : ObjectId("5a498d86f0ec47e9f5ce2db4"), "name" : "zhangsan", "age" : 10 }
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$size
根据数组长度筛选
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| db.mydemo.insert({myarray:[1,2,3,4]});
db.mydemo.insert({myarray:[1,2,3]});
db.mydemo.insert({myarray:[1,2,3,5]});
> db.mydemo.find({myarray: {$size: 3}})
{ "_id" : ObjectId("5a4999d8f26cb8a9ec47407e"), "myarray" : [ 1, 2, 3 ] }
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/a/
查询某个字段包含字符
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| > db.personalinfo.find({name:/a/})
{ "_id" : ObjectId("5a498d86f0ec47e9f5ce2db4"), "name" : "zhangsan", "age" : 10 }
{ "_id" : ObjectId("5a498d87f0ec47e9f5ce2db6"), "name" : "wangsu", "age" : 12 }
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$where
$where比较常用在一些复杂的查询条件，它的内容是一个JavaScript的代码表达式。
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| > db.personalinfo.find({$where: 'this.age > 10'});
{ "_id" : ObjectId("5a498d86f0ec47e9f5ce2db5"), "name" : "lisi", "age" : 11 }
{ "_id" : ObjectId("5a498d87f0ec47e9f5ce2db6"), "name" : "wangsu", "age" : 12 }
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分页
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| > db.personalinfo.find().count();
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> db.personalinfo.find().skip(1);
{ "_id" : ObjectId("5a498d86f0ec47e9f5ce2db5"), "name" : "lisi", "age" : 11 }
{ "_id" : ObjectId("5a498d87f0ec47e9f5ce2db6"), "name" : "wangsu", "age" : 12 }
> db.personalinfo.find().limit(2);
{ "_id" : ObjectId("5a498d86f0ec47e9f5ce2db4"), "name" : "zhangsan", "age" : 10 }
{ "_id" : ObjectId("5a498d86f0ec47e9f5ce2db5"), "name" : "lisi", "age" : 11 }
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count()默认是统计整个文档的数量，要根据之前的条件统计，需要加上参数true。
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| > db.personalinfo.find().limit(2).count();
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> db.personalinfo.find().limit(2).count(true);
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查询就介绍到这里，后面的文章将继续介绍MongoDB的聚合操作。