Question

Following MongoDB documentation example seems to be wrong.

Any suggestion?

a== 1 and a >5 will never match any document.

Link

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

In the above example documents with an element of a having a value of a equal to 1 and a value of a greater than 5 will be returned

Answer 1

You are missing an import line in the example:

db.foo.insert( { a: [ 1, 10 ] } )
db.foo.find( { $and: [ { a: 1 }, { a: { $gt: 5 } } ] } )

The insert will give you a record looking like the following:

{"a" : [1, 10] , 
 "_id"  : "497ce4051ca9ca6d3efca323"}

So the find will return any result where a == 1 and a also has a value greater than 5. In this case, a can be two values: http://www.mongodb.org/display/DOCS/Multikeys

The a is 1, and at the same time 10. So that is why this query would return this result.