MongoDB-解释有关db.collection.find()方法的查询计划的信息
有关查询计划的信息，请explain()在MongoDB中使用。让我们创建一个包含文档的集合-
> db.demo637.ensureIndex({ClientName:1});
{
"createdCollectionAutomatically" : true,
"numIndexesBefore" : 1,
"numIndexesAfter" : 2,
"ok" : 1
}
> db.demo637.insert({ClientName:"John"});
WriteResult({ "nInserted" : 1 })
> db.demo637.insert({ClientName:"Bob"});
WriteResult({ "nInserted" : 1 })
> db.demo637.insert({ClientName:"Johnson"});
WriteResult({ "nInserted" : 1 })在find()方法的帮助下显示集合中的所有文档-
> db.demo637.find();
这将产生以下输出-
{ "_id" : ObjectId("5e9c26916c954c74be91e6db"), "ClientName" : "John" }
{ "_id" : ObjectId("5e9c26936c954c74be91e6dc"), "ClientName" : "Bob" }
{ "_id" : ObjectId("5e9c269d6c954c74be91e6dd"), "ClientName" : "Johnson" }案例1-
这是对regexp的查询//-
> db.demo637.find({ClientName:/john/}).explain();这将产生以下输出-
{
"queryPlanner" : {
"plannerVersion" : 1,
"namespace" : "test.demo637",
"indexFilterSet" : false,
"parsedQuery" : {
"ClientName" : {
"$regex" : "john"
}
},
"winningPlan" : {
"stage" : "FETCH",
"inputStage" : {
"stage" : "IXSCAN",
"filter" : {
"ClientName" : {
"$regex" : "john"
}
},
"keyPattern" : {
"ClientName" : 1
},
"indexName" : "ClientName_1",
"isMultiKey" : false,
"multiKeyPaths" : {
"ClientName" : [ ]
},
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "forward",
"indexBounds" : {
"ClientName" : [
"[\"\", {})",
"[/john/, /john/]"
]
}
}
},
"rejectedPlans" : [ ]
},
"serverInfo" : {
"host" : "DESKTOP-QN2RB3H",
"port" : 27017,
"version" : "4.0.5",
"gitVersion" : "3739429dd92b92d1b0ab120911a23d50bf03c412"
},
"ok" : 1
}案例2-
以下是对regexp/^/−的查询
> db.demo637.find({ClientName:/^john/}).explain();这将产生以下输出-
{
"queryPlanner" : {
"plannerVersion" : 1,
"namespace" : "test.demo637",
"indexFilterSet" : false,
"parsedQuery" : {
"ClientName" : {
"$regex" : "^john"
}
},
"winningPlan" : {
"stage" : "FETCH",
"inputStage" : {
"stage" : "IXSCAN",
"keyPattern" : {
"ClientName" : 1
},
"indexName" : "ClientName_1",
"isMultiKey" : false,
"multiKeyPaths" : {
"ClientName" : [ ]
},
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "forward",
"indexBounds" : {
"ClientName" : [
"[\"john\", \"joho\")",
"[/^john/, /^john/]"
]
}
}
},
"rejectedPlans" : [ ]
},
"serverInfo" : {
"host" : "DESKTOP-QN2RB3H",
"port" : 27017,
"version" : "4.0.5",
"gitVersion" : "3739429dd92b92d1b0ab120911a23d50bf03c412"
},
"ok" : 1
}