Mongo_自定义查询补充-【官方】百战程序员_IT在线教育培训机构


xxxxxxxxxx
db.person.find({$where:function(){return this.age>20}}) # 5.0版本不能用了
db.person.find({$where:"this.age==23"});
db.person.find("this.age >23");
db.person.find('this.country=="吴国" || this.age==23');

limit

用于读取指定数量的文档


xxxxxxxxxx
db.集合名称.find().limit(NUMBER)

skip

用于跳过指定数量的文档


xxxxxxxxxx
db.集合名称.find().skip(2)

sort

用于对结果集进行排序


xxxxxxxxxx
db.集合名称.find().sort({字段:1,...})

参数1为升序排列
参数-1为降序排列

count

用于统计结果集中文档条数


x
db.集合名称.find({条件}).count()
db.集合名称.count({条件})

db.stu.find({gender:true}).count()
db.stu.count({age:{$gt:20},gender:true})

$exists

判断是否有某个字段


xxxxxxxxxx
db.集合名称.find({'field':{$exists:true}})

dictinct

去重


xxxxxxxxxx
db.集合名称.distinct(field)
db.集合名称.distinct(field,{过滤条件  })

样例数据

首先插入一批文档，再进行查询


xxxxxxxxxx
db.person.insert([{"name":"司马懿","country":"魏国","age":35},
{"name":"张辽","country":"魏国","age":34},
{"name":"徐晃","country":"魏国","age":24},
{"name":"夏侯惇","country":"魏国","age":23},
{"name":"夏侯渊","country":"魏国","age":23},
{"name":"庞德","country":"魏国","age":23},
{"name":"张郃","country":"魏国","age":34},
{"name":"李典","country":"魏国","age":41},
{"name":"乐进","country":"魏国","age":34},
{"name":"典韦","country":"魏国","age":12},
{"name":"曹洪","country":"魏国","age":21},
{"name":"曹仁","country":"魏国","age":11},
{"name":"诸葛亮","country":"蜀国","age":20},
{"name":"关羽","country":"蜀国","age":32},
{"name":"张飞","country":"蜀国","age":23},
{"name":"马超","country":"蜀国","age":53},
{"name":"黄忠","country":"蜀国","age":23},
{"name":"赵云","country":"蜀国","age":32},
{"name":"魏延","country":"蜀国","age":42},
{"name":"关平","country":"蜀国","age":12},
{"name":"周仓","country":"蜀国","age":42},
{"name":"关兴","country":"蜀国","age":23},
{"name":"张苞","country":"蜀国","age":12},
{"name":"周瑜","country":"吴国","age":32},
{"name":"吕蒙","country":"吴国","age":11},
{"name":"甘宁","country":"吴国","age":23},
{"name":"太史慈","country":"吴国","age":23},
{"name":"程普","country":"吴国","age":24},
{"name":"黄盖","country":"吴国","age":28},
{"name":"韩当","country":"吴国","age":23},
{"name":"周泰","country":"吴国","age":29},
{"name":"蒋钦","country":"吴国","age":19},
{"name":"丁奉","country":"吴国","age":17},
{"name":"徐盛","country":"吴国","age":27}
])

实时效果反馈

1.MongoDB查询集合所有文档的命令是？

A db.collection.find({id:0})

B db.collection.findAll()

C db.collection.find({})

D 以上都不对

答案

1=>C

Mongo_文档的查询 Mongo_聚合操作分组与过滤

北京市昌平区回龙观镇南店村综合商业楼2楼226室