MongoDB Database command operation (ii)

Now learn more about MongoDB's database operations.

Query statements

Db.xxx (collection name). Find () # query Db.xxx (collection name). FindOne () # returns only one Db.xxx (collection name). FindOne (). Pretty () # return result formatted # comparison operator equals, The default is equal to the judgment, there are no operators, such as: Db.xxx (collection name). Find ({name: "Xiao"}) is less than $lt, such as: Db.xxx (collection name). Find ({age:{$lt: 30}}) less than or equal to $lte, such as: Db.xxx (collection name). Find ({age:{$lte: 30}}) is greater than $GT, such as: Db.xxx (collection name). Find ({age:{$gt: 30}}) is greater than or equal to $gte, such as: Db.xxx (collection name). Find ({age:{$gte: 30}}) is not equal to $ne, such as: Db.xxx (collection name). Find ({age:{$ne: 30}) # logical operator, which is the multi-condition query Db.xxx (collection name). Find ({age:{$ne: 30 }, Name: "Xiaoming"}) # Default logic with Db.xxx (collection name). Find ({$or: [{age:{$ne: +}, Name: "Xiaoming"}]}) # Default logical OR # Range query Db.xxx (collection name). Find ({age:{$in: [18,30]}) # Db.xxx (collection name) in a range. Find ({age:{$nin: [18,30]}}) # is not in a range # regular $regexdb.xxx (collection name). Find ({ name:{$regex: "^x"}) # function query $where, use this to represent this collection db.xxx (collection name). Find ({$where: function () {return This.age < 10}}) # Limit the number of returns DB.XXX (collection name). Find (). Limit (3) # query offset db.xxx (collection name). Find (). Skip (3) # returns # loop for (i=0;i<15;i++) {db.xxx starting from 4th) Collection name). Insert ({_id:i*2})}# the query returns some fields that need to return a setting of 1 and do not need to set 0db.xxx (collection name). Find ({},{name:1,age:0}) # Sort (), 1-bit ascending, 1 to descending DB.xxx (collection name). Find (). Sort ({name:-1}) # returns the number of Count () db.xxx (collection name). Count ({name: "Xiaoming"}) # go to Heavy db.xxx (set name). Distinct ("name", {})

Aggregation functions

• Syntax: DB. Collection name. Aggregate ({pipe: {expression}})

# 管道$group：将集合中的文档分组，可用于统计结果$match：过滤数据，只输出符合条件的文档$project：修改输入文档的结构，如重命名、增加、删除字段、创建计算结果$sort：将输入文档排序后输出$limit：限制聚合管道返回的文档数$skip：跳过指定数量的文档，并返回余下的文档$unwind：将数组类型的字段进行拆分# 表达式$sum：计算总和，$sum:1同count表示计数$avg：计算平均值$min：获取最小值$max：获取最大值$push：在结果文档中插入值到一个数组中$first：根据资源文档的排序获取第一个文档数据$last：根据资源文档的排序获取最后一个文档数据

Index

• 1 means ascending,-1 means descending

• Syntax structure: DB. Collection_name.ensureindex (Keys[,options])

keys，要建立索引的参数列表。如：{KEY:1}，其中key表示字段名，1表示升序排序，也可使用使用数字-1降序。options，可选参数，表示建立索引的设置。可选值如下：background，Boolean，在后台建立索引，以便建立索引时不阻止其他数据库活动。默认值 false。unique，Boolean，创建唯一索引。默认值 false。name，String，指定索引的名称。如果未指定，MongoDB会生成一个索引字段的名称和排序顺序串联。dropDups，Boolean，创建唯一索引时，如果出现重复删除后续出现的相同索引，只保留第一个。sparse，Boolean，对文档中不存在的字段数据不启用索引。默认值是 false。v，index version，索引的版本号。weights，document，索引权重值，数值在 1 到 99,999 之间，表示该索引相对于其他索引字段的得分权重。

# 创建普通索引db.集合.ensureIndex({属性:1})# 创建唯一索引，实现唯一约束的功能db.集合.ensureIndex({"name":1},{"unique":true})# 创建联合索引db.集合.ensureIndex({name:1,age:1})#查看集合所有索引db.集合.getIndexes()# 删除索引db.集合.dropIndex(‘索引名称‘)db.集合.dropIndexs() # 删除集合所有的索引

MongoDB Database command operation (ii)