使用NodeJS，MySQL测量查询执行时间

Question

I am trying to write script that will measure execution time for query. For now I have script that I will include at the end of the question, but it seems that she collects results, add result on previous etc. So I wanted to ask you, do you maybe now how can I avoid that, where do I make a mistake?

var mysql = require('mysql');
var client = mysql.createConnection({
user: 'root',
password: '',
database: 'kong_centar'
//debug: true  
});

var ignore = [mysql.ERROR_DB_CREATE_EXISTS,
          mysql.ERROR_TABLE_EXISTS_ERROR];

client.on('error', function (err) {
if (ignore.indexOf(err.number) + 1) { return; }
throw err;
});
for(i=0; i<10; i++){
var pre_query = new Date().getTime();
client.query('select * from korisnik', function(err, result, fields){
    var post_query = new Date().getTime();
    var duration = (post_query - pre_query) / 1000;

    console.log(duration);

    if (err)
    {
        throw err;
    }
    else
    {

        //console.log(result);
        for (var i in result)
        {
            //var people = result[i];
            //console.log(people.firstname + ' ' + people.lastname);
        }
    }
});
}
client.end();

Answer 1

You are experiencing a well know problem, when functions are created within a loop. In essence, all functions will point to the same variable (pre_query). Have a look at this question for a description of the problem and a solution.