Covered queries
db.cities.find(
{ population: { $gte: 2000000 }, elevation: { $gte : 1654 } }
).explain();
"winningPlan" : {
*"stage" : "FETCH",*
"inputStage" : {
"stage" : "IXSCAN",
"keyPattern" : { "population" : 1, "elevation" : 1 },
}
},
vs.
db.cities.find(
{ population: { $gte: 2000000 }, elevation: { $gte : 1654 } },
{ _id: 0, population: 1, elevation: 1 }
).explain();
"winningPlan" : {
*"stage" : "PROJECTION",*
"transformBy" : { "_id" : 0, "population" : 1, "elevation" : 1 },
"inputStage" : {
"stage" : "IXSCAN",
"keyPattern" : { "population" : 1, "elevation" : 1 },
}
},