Node JS MySQL查询函数不返回结果

Question

I am running a MySQL query inside a .js file running on Node JS. I have the connection setup ok and the query works but when I try returning the result back to the original call it doesn't seem to work.

 function sqlQuery(query){ console.log("Running query"); var conn = connection(); var result = false; conn.query(query, function(err, rows, fields) { conn.end(); if (!err){ result = rows; } else { result = err; } }); return result; } var loginResult = sqlQuery("SELECT * FROM `players`"); console.log(loginResult);

If I use the following code it does write the result to the console inside the query but not the final "loginResult". I am not getting any errors so my question is - is there an error in the way I am getting the returned result?

 if (!err){ result = rows; console.log(rows); } else { result = err; }

Answer 1

Virtually everything in Node.js is asynchronous, and SQL query functions definitely are. You're calling conn.query(query, callback) , which means that query is called, and then once there is a result at some point in the future, your callback function gets called with the result for you to work with. So:

conn.query(query, function runThisEventually(err, rows, fields) {
    if (err) {
      console.error("One or more errors occurred!");
      console.error(err);
      return;
    }
    processResults(rows, fields);
});

You won't get the result immediately after calling conn.query(...) , so your code gets to do "other things" in the mean time, and at some point, your callback will be triggered and you can pick up result processing there.

Answer 2

conn.query(query, function(err, rows, fields) {
    if (err) 
        console.log("error ocurred",err);
    res.send({
        "code":400,
        "message":"error ocurred"
    })
});