Node.js and mysql Callback : query in query callback

Question

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();

Answer 1

You db.end() call will queue the connection to close once the SELECT has completed, so when you attempt to do the inner INSERT query, the database connection will have been closed, hence the error PROTOCOL_ENQUEUE_AFTER_QUIT, as you are attempting to queue a new command after the connection is closed.

Depending on how you are creating the connection, you should either move your db.end() call inside the callbacks, or not have a db.end() call at all if the connection is opened on program start.