All I want to do is insert some data if my database doesn't have that, so I put Insert SQL into my callback function of my Select SQL, but I got error like this:

{ [Error: Cannot enqueue Query after invoking quit.] code: 'PROTOCOL_ENQUEUE_AFTER_QUIT', fatal: false }

my code snippet is here:

db.query('SELECT count(*) as Resultcount FROM tablename WHERE email = ? and password = ?', [post.email, post.password], function(error, result){

    if (result[0].Resultcount == 0){

        var query2 = db.query('INSERT INTO tablename SET ?', [post], function(err, result) {

            if(err){

              console.log(err);

           }

             console.log(result);

          });

    }

    else{

        console.log('have data already');

    }

});

Could someone give me some advice?
Thanks

----update----

actually, the callback function of select SQL is not an anonymous function, my code snippet about db.end() is like this:

var QueryResults = new queryResultFuntion(Back_results);



    db.query('SELECT count(*) as Resultcount FROM tablename WHERE email = ? and password = ?', [post.email, post.password], QueryResults.queryResult );





    db.end();