MongoDB 索引创建和查询优化的方法

db.inventory.insertMany( [
   { item: "journal", qty: 25, size: { h: 14, w: 21, uom: "cm" }, status: "A" },
   { item: "notebook", qty: 50, size: { h: 8.5, w: 11, uom: "in" }, status: "A" },
   { item: "paper", qty: 100, size: { h: 8.5, w: 11, uom: "in" }, status: "D" },
   { item: "planner", qty: 75, size: { h: 22.85, w: 30, uom: "cm" }, status: "D" },
   { item: "postcard", qty: 45, size: { h: 10, w: 15.25, uom: "cm" }, status: "A" }
]);

use testdb
for(var i =1; i<10; i++) db.users.insert({id:i,name: "zhangsan"+i,age: 100+i})

最简单的查询语句为：db.customers.find()，按照插入的顺序返回前20个文档，如果 记录总数比20大，则我们可以通过命令“it”获取更多文档。 
> db.users.find({id:9}) 
精确匹配选择器，返回包含键值对id:9的文档。 
> db.users.find({name:"xiaoming",age:101}) 
精确匹配选择器，但查询条件是要返回同时匹配键值对{name:"xiaoming",age:101}的文档。 
> db.users.find({age:{$lt:102}}) 
$lt表示的是小于 
> db.users.find({age:{$lte:102}}) 
$lte表示的小于或等于 
> db.users.find({age:{$gt:105}}) 
$gt表示的是大于 
> db.users.find({age:{$gte:105}}) 
$gte表示的是大于或等于 
> db.users.find({age:{$lt:120,$gte:105}}) 
范围选择器，age:{$lt:120,$gte:119}表示的是小于120，大于或等于119 
> db.users.find({id:{$in:[1,2]}}) 
表示返回key的值在某些value范围内 
> db.users.find({id:{$nin:[1,2]}}) 
$nin表示返回key的值不在某些value范围内，$nin是一种比较低效的査询选择器，它会进行全表扫描，因此最好不要单独使用$nin 
> db.users.find({id:{$ne:1}}) 
$ne表示不等于。单独使用$ne，它也不会利用索引的优势，反而会进行全表扫描，我们最好与其他查询选择器配合使用。 
> db.users.find({$or:[{id:11},{age:109}] }）
$or表示或运算的选择器，主要用于对两个不同key对应的文档进行连接。 
> db.users.find({$and:[{id:1},{age:109}]}) 
$and表示与运算的选择器，对于两个不同的key,要同时满足条件。 
> db.users.find({id:{$exists:ture}}) 
$exists与关系数据库中的exists不一样，因为MongoDB的表结构不是固定的，有的时候需要返回包含有某个字段的所有记录或者不包含某个字段的所有记录。

for(var i = 1;i < 10;i++) db.custoners.insert({name:"zhangsan"+i,province:"liaoning"})
for(var i = 1;i < 10;i++) db.customers.insert({name:"lisi"+i,province:"fujian"})
for(var i = 1;i < 10;i++) db.customers.insert({name:"niuer"+i,province:"guangdong"})
for(var i = 1;i < 10;i++) db.customers.insert({name:"wangwu"+i,province:"Hunan"})
for(var i = 1;i < 10;i++) db.customers.insert({name:"liyi"+i,province:"Sichuan"})

> db.customers.find({"name" : "liyi6", "province" : "Sichuan"}).explain()
{
	"explainVersion" : "1",
	"queryPlanner" : {
		"namespace" : "sample_mflix.customers",
		"indexFilterSet" : false,
		"parsedQuery" : {
			"$and" : [
				{
					"name" : {
						"$eq" : "liyi6"
					}
				},
				{
					"province" : {
						"$eq" : "Sichuan"
					}
				}
			]
		},
		"queryHash" : "AE1EB7A5",
		"planCacheKey" : "C0AA3338",
		"maxIndexedOrSolutionsReached" : false,
		"maxIndexedAndSolutionsReached" : false,
		"maxScansToExplodeReached" : false,
		"winningPlan" : {
			"stage" : "FETCH",
			"inputStage" : {
				"stage" : "IXSCAN",
				"keyPattern" : {
					"name" : 1,
					"province" : 1
				},
				"indexName" : "name_1_province_1",
				"isMultiKey" : false,
				"multiKeyPaths" : {
					"name" : [ ],
					"province" : [ ]
				},
				"isUnique" : false,
				"isSparse" : false,
				"isPartial" : false,
				"indexVersion" : 2,
				"direction" : "forward",
				"indexBounds" : {
					"name" : [
						"[\"liyi6\", \"liyi6\"]"
					],
					"province" : [
						"[\"Sichuan\", \"Sichuan\"]"
					]
				}
			}
		},
		"rejectedPlans" : [ ]
	},
	"command" : {
		"find" : "customers",
		"filter" : {
			"name" : "liyi6",
			"province" : "Sichuan"
		},
		"$db" : "sample_mflix"
	},
	"serverInfo" : {
		"host" : "13727b89dec5",
		"port" : 27017,
		"version" : "5.0.5",
		"gitVersion" : "d65fd89df3fc039b5c55933c0f71d647a54510ae"
	},
	"serverParameters" : {
		"internalQueryFacetBufferSizeBytes" : 104857600,
		"internalQueryFacetMaxOutputDocSizeBytes" : 104857600,
		"internalLookupStageIntermediateDocumentMaxSizeBytes" : 104857600,
		"internalDocumentSourceGroupMaxMemoryBytes" : 104857600,
		"internalQueryMaxBlockingSortMemoryUsageBytes" : 104857600,
		"internalQueryProhibitBlockingMergeOnMongoS" : 0,
		"internalQueryMaxAddToSetBytes" : 104857600,
		"internalDocumentSourceSetWindowFieldsMaxMemoryBytes" : 104857600
	},
	"ok" : 1
}

> for(var i = 1;i < 10;i++) db.ccustomers.insert({name:"liyi"+i,"tags": ["sports", "music", "movies"]})
WriteResult({ "nInserted" : 1 })
> for(var i = 1;i < 10;i++) db.ccustomers.insert({name:"liyao"+i,"tags": ["sports", "movies","games","read"]})
WriteResult({ "nInserted" : 1 })
> for(var i = 1;i < 10;i++) db.ccustomers.insert({name:"lisi"+i,"tags": ["sports", "music", "movies"]})
WriteResult({ "nInserted" : 1 })
> for(var i = 1;i < 10;i++) db.ccustomers.insert({name:"liyiyi"+i,"tags": ["sports",  "movies","write"]})
WriteResult({ "nInserted" : 1 })
> db.ccustomers.createIndex({"tags":1})
{
	"numIndexesBefore" : 1,
	"numIndexesAfter" : 2,
	"createdCollectionAutomatically" : false,
	"ok" : 1
}

db.setProfilingLevel(level,[ slowms]) 

> db.setProfilingLevel(2)
{ "was" : 0, "slowms" : 100, "sampleRate" : 1, "ok" : 1 }
> db.system.profile.find()