Aggregation Framework - Order of $limit and $skip is important

[mongo-php]

Hey Group,

why is there a difference between

db.runCommand( { aggregate: "weather", pipeline: [

{$match : { "days" : { $exists: true} }},

{$limit : 100},

{$project : {

name : 1,

sum : { $add:["$days.4", "$days.4","$days.9"] }

}},

{ $skip : 10 },

{ $limit : 10 },

{ $sort : { sum : -1}},

]);

and

db.runCommand( { aggregate: "weather", pipeline: [

{$match : { "days" : { $exists: true} }},

{$limit : 100},

{$project : {

name : 1,

sum : { $add:["$days.4", "$days.4","$days.9"] }

}},

        { $limit : 10 } ,

{ $skip : 10 },

{ $sort : { sum : -1}},

]);

The result from both commands differs.

Is this caused by the pipelining ?

[Eliot Horowitz]

Order is relevant.

If you say,
skip 10, then limit 10
you'll get 11-20

if you say
limit 10
skip 10

you'll get nothing

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