generate unique random number in mongoose db without repeat?

You could generate your random number and check that it is not already stored:

function getNumber(callback){    var n = Math.floor(Math.random()*1000000000);    YourModel.findOne({'number': n}, function(err, result){        if (err) callback(err);        else if (result) return getNumber(callback);        else callback(null, n);    });}getNumber(function(error, number){    console.log(number);});

If you think this process could be called more than once in parallel, you should do some additional checks:

var alreadyRuning = false;function getNumber(callback){    if (alreadyRuning) return setTimeout(function(){        getNumber(callback);    }, 10);    alreadyRuning = true;    var n = Math.floor(Math.random()*1000000000);    YourModel.findOne({'number': n}, function(err, result){        if (err) callback(err);        else {            alreadyRuning = false;            if (result) return getNumber(callback);            else callback(null, n);        }    });}getNumber(function(error, number){    console.log(number);    //...    YourModel.insert({'number': n}, function(err, result){        if (!err) alreadyRuning = false    });});

I don't believe it is possible to do this on the database, like your SQL-example.There is a ticket for adding a $rand operator to the aggregation pipeline, but that ticket is still unresolved:

https://jira.mongodb.org/browse/SERVER-30405

Still, you could create a database-function (which can have a bad performance) and store it on the server: https://docs.mongodb.com/manual/tutorial/store-javascript-function-on-server/

That's not really a mongoose solution, though.