#MongoDB使用： 条件操作，排序，索引，分页查询，聚合函数##mongodb条件查询 > use study switched to db study > db.student.insert({"name":"张三","age":18,"score":100,"sex":1}) WriteResult({ "nInserted" : 1 }) > db.student.insert({"name":"李四","age":20,"score":90,"sex":1}) WriteResult({ "nInserted" : 1 }) > db.student.insert({"name":"小红","age":19,"score":100,"sex":0}) WriteResult({ "nInserted" : 1 }) > db.student.insert({"name":"小明","age":19,"score":95,"sex":1}) WriteResult({ "nInserted" : 1 })首先要创建一个study数据库，并创建student集合，存入四条数据。 ```shell script1. 查询年龄大于19的学生。‘>‘==>‘gt‘ // ‘>=‘==>‘gte‘> db.student.find({"age":{$gt:19}}){ "_id" : ObjectId("5ea502960cf4f3a59d7d9850"), "name" : "李四", "age" : 20, "score" : 90, "sex" : 1 }2. 查询成绩小于等于95的学生 ‘<‘==>‘lt‘ // ‘<=‘==>‘lte‘> db.student.find({"score":{$lte: 95}}){ "_id" : ObjectId("5ea502960cf4f3a59d7d9850"), "name" : "李四", "age" : 20, "score" : 90, "sex" : 1 }{ "_id" : ObjectId("5ea502c70cf4f3a59d7d9852"), "name" : "小明", "age" : 19, "score" : 95, "sex" : 1 }3. 查询年龄在18-20之间的。 where age>18 and age <20> db.student.find({"age":{$lt:20,$gt:18}}){ "_id" : ObjectId("5ea502ae0cf4f3a59d7d9851"), "name" : "小红", "age" : 19, "score" : 100, "sex" : 0 }{ "_id" : ObjectId("5ea502c70cf4f3a59d7d9852"), "name" : "小明", "age" : 19, "score" : 95, "sex" : 1 }```#分页查询db.collection.find(query).limit(number)查询两条数据```shell script> db.student.find(){ "_id" : ObjectId("5ea502830cf4f3a59d7d984f"), "name" : "张三", "age" : 18, "score" : 100, "sex" : 1 }{ "_id" : ObjectId("5ea502960cf4f3a59d7d9850"), "name" : "李四", "age" : 20, "score" : 90, "sex" : 1 }{ "_id" : ObjectId("5ea502ae0cf4f3a59d7d9851"), "name" : "小红", "age" : 19, "score" : 100, "sex" : 0 }{ "_id" : ObjectId("5ea502c70cf4f3a59d7d9852"), "name" : "小明", "age" : 19, "score" : 95, "sex" : 1 }> db.student.find().limit(2){ "_id" : ObjectId("5ea502830cf4f3a59d7d984f"), "name" : "张三", "age" : 18, "score" : 100, "sex" : 1 }{ "_id" : ObjectId("5ea502960cf4f3a59d7d9850"), "name" : "李四", "age" : 20, "score" : 90, "sex" : 1 }```##跳过skip查询第2-3条数据```shell script> db.student.find().limit(2).skip(1){ "_id" : ObjectId("5ea502960cf4f3a59d7d9850"), "name" : "李四", "age" : 20, "score" : 90, "sex" : 1 }{ "_id" : ObjectId("5ea502ae0cf4f3a59d7d9851"), "name" : "小红", "age" : 19, "score" : 100, "sex" : 0 }```通过使用skip和limit我们可以进行分页查询。先在集合中插入10条记录。```shell script> db.student.find(){ "_id" : ObjectId("5ea502830cf4f3a59d7d984f"), "name" : "张三", "age" : 18, "score" : 100, "sex" : 1 }{ "_id" : ObjectId("5ea502960cf4f3a59d7d9850"), "name" : "李四", "age" : 20, "score" : 90, "sex" : 1 }{ "_id" : ObjectId("5ea502ae0cf4f3a59d7d9851"), "name" : "小红", "age" : 19, "score" : 100, "sex" : 0 }{ "_id" : ObjectId("5ea502c70cf4f3a59d7d9852"), "name" : "小明", "age" : 19, "score" : 95, "sex" : 1 }{ "_id" : ObjectId("5ea508010cf4f3a59d7d9853"), "name" : "王二", "age" : 22, "score" : 88, "sex" : 1 }{ "_id" : ObjectId("5ea508140cf4f3a59d7d9854"), "name" : "马六", "age" : 21, "score" : 88, "sex" : 0 }{ "_id" : ObjectId("5ea508280cf4f3a59d7d9855"), "name" : "小芳", "age" : 18, "score" : 88, "sex" : 0 }{ "_id" : ObjectId("5ea5083a0cf4f3a59d7d9856"), "name" : "小李", "age" : 18, "score" : 93, "sex" : 1 }{ "_id" : ObjectId("5ea5084a0cf4f3a59d7d9857"), "name" : "小张", "age" : 18, "score" : 98, "sex" : 1 }{ "_id" : ObjectId("5ea5085d0cf4f3a59d7d9858"), "name" : "小强", "age" : 22, "score" : 70, "sex" : 1 }```查询第3页数据，每页3条。 db.collection.find().limit(3).skip((3-1)*3) <==> limit (x-1)*3, 3;```shell script> db.student.find().skip(2*3).limit(3){ "_id" : ObjectId("5ea508280cf4f3a59d7d9855"), "name" : "小芳", "age" : 18, "score" : 88, "sex" : 0 }{ "_id" : ObjectId("5ea5083a0cf4f3a59d7d9856"), "name" : "小李", "age" : 18, "score" : 93, "sex" : 1 }{ "_id" : ObjectId("5ea5084a0cf4f3a59d7d9857"), "name" : "小张", "age" : 18, "score" : 98, "sex" : 1 }```##排序还是上面的集合，按照年龄升序排序。 db.collection.find(query).sort({key:1}) 1表示升序，-1表示降序```shell script> db.student.find().sort({age:1}){ "_id" : ObjectId("5ea502830cf4f3a59d7d984f"), "name" : "张三", "age" : 18, "score" : 100, "sex" : 1 }{ "_id" : ObjectId("5ea508280cf4f3a59d7d9855"), "name" : "小芳", "age" : 18, "score" : 88, "sex" : 0 }{ "_id" : ObjectId("5ea5083a0cf4f3a59d7d9856"), "name" : "小李", "age" : 18, "score" : 93, "sex" : 1 }{ "_id" : ObjectId("5ea5084a0cf4f3a59d7d9857"), "name" : "小张", "age" : 18, "score" : 98, "sex" : 1 }{ "_id" : ObjectId("5ea502ae0cf4f3a59d7d9851"), "name" : "小红", "age" : 19, "score" : 100, "sex" : 0 }{ "_id" : ObjectId("5ea502c70cf4f3a59d7d9852"), "name" : "小明", "age" : 19, "score" : 95, "sex" : 1 }{ "_id" : ObjectId("5ea502960cf4f3a59d7d9850"), "name" : "李四", "age" : 20, "score" : 90, "sex" : 1 }{ "_id" : ObjectId("5ea508140cf4f3a59d7d9854"), "name" : "马六", "age" : 21, "score" : 88, "sex" : 0 }{ "_id" : ObjectId("5ea508010cf4f3a59d7d9853"), "name" : "王二", "age" : 22, "score" : 88, "sex" : 1 }```##索引 createIndex(key,options)```shell script> db.student.createIndex({"score":1}){ "createdCollectionAutomatically" : false, "numIndexesBefore" : 1, "numIndexesAfter" : 2, "ok" : 1}```{"score":1},表示创建score的索引，升序排序。还可以写复合索引{"score":1,"age":-1}## 聚合查询男女生数量，男为1,女为0```shell script> db.student.aggregate([{$group:{"_id":"$sex",num_tutorial:{$sum:1}}}]){ "_id" : 0, "num_tutorial" : 3 }{ "_id" : 1, "num_tutorial" : 7 }``` 