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Asked: 2026-06-11T13:07:56+00:00

Can someone tell me the difference between these two queries? db.foo.find({ $and: [{a: 1},

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Can someone tell me the difference between these two queries?

db.foo.find({ $and: [{a: 1}, {a: {$gt: 5}}]})

and

db.foo.find({a:1, a:{$gt:5}})

EDIT
Ok let me change the question a little bit. Assume the following

dev(mongod-2.2.0)>db.foo.insert({UserID: 1, Status:'unread' })
dev(mongod-2.2.0)>db.foo.insert({UserID: 1, Status:'unread' })
dev(mongod-2.2.0)>db.foo.insert({UserID: 1, Status:'unread' })
dev(mongod-2.2.0)>db.foo.insert({UserID: 1, Status:'unread' })
dev(mongod-2.2.0)>db.foo.insert({UserID: 1, Status:'unread' })
dev(mongod-2.2.0)>db.foo.insert({UserID: 1, Status:'unread' })
dev(mongod-2.2.0)>db.foo.insert({UserID: 1, Status:'unread' })
dev(mongod-2.2.0)>db.foo.insert({UserID: 1, Status:'unread' })

And I want to find all unread messages for user id 1. Do I do this

db.foo.find({UserID:1, Status:'unread'})

or this

db.foo.find({$and: [{UserID:1},{Status:'unread']})
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1 Answer

  1. Editorial Team

    With $and both conditions are taken into account when querying. Without $and only the last spec for a is considered in the query. This seems to happen with insert from mongo shell also.

    In your edited question, I would definitely use db.foo.find({UserID:1, Status:'unread'})

    Example below:

    > db.sotest.insert({a : 1})
> db.sotest.insert({a : 2})
> db.sotest.insert({a : 6})
> db.sotest.insert({a : 7})
> db.sotest.insert({a : [1, 7]})
> db.sotest.find()
{ "_id" : ObjectId("50587c0164433af6a99c988f"), "a" : 1 }
{ "_id" : ObjectId("50587c0564433af6a99c9890"), "a" : 2 }
{ "_id" : ObjectId("50587c0d64433af6a99c9891"), "a" : 6 }
{ "_id" : ObjectId("50587c1064433af6a99c9892"), "a" : 7 }
{ "_id" : ObjectId("50587c1f64433af6a99c9893"), "a" : [ 1, 7 ] }
> db.sotest.find({a:1, a:{$gt:5}})
{ "_id" : ObjectId("50587c0d64433af6a99c9891"), "a" : 6 }
{ "_id" : ObjectId("50587c1064433af6a99c9892"), "a" : 7 }
{ "_id" : ObjectId("50587c1f64433af6a99c9893"), "a" : [ 1, 7 ] }
> db.sotest.find({a:{$gt:5}, a:1})
{ "_id" : ObjectId("50587c0164433af6a99c988f"), "a" : 1 }
{ "_id" : ObjectId("50587c1f64433af6a99c9893"), "a" : [ 1, 7 ] }
> db.sotest.find({$and : [{a:{$gt:5}}, {a:1}]})
{ "_id" : ObjectId("50587c1f64433af6a99c9893"), "a" : [ 1, 7 ] }
>
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