做了一个nodejs并发测试，先描述一下环境 数据库mysql,大概两张表，读取第一张表test的数据，拿出来-1，存到第二张testlog表记录一下，用jmeter同事模拟50个请求，结果发现，部分数据没有-1成功

test 表数据

id 		num 		desc

1		 94 		2017-02-28 14:41:17:86

testlog 表数据

id, testid, num, desc

4	1	99	2017-02-28 14:32:42:28

5	1	98	2017-02-28 14:32:43:76

6	1	97	2017-02-28 14:32:44:89

7	1	97	2017-02-28 14:32:44:88

8	1	97	2017-02-28 14:32:44:28

9	1	97	2017-02-28 14:32:44:86

10	1	97	2017-02-28 14:32:44:45

11	1	97	2017-02-28 14:32:45:48

12	1	97	2017-02-28 14:32:45:49

推测可能是同时修改数据，某一个现在没有修改完毕，下一个线程已经读取过了，导致数据更新不一致，但是nodejs不都是单线程的吗，请各位大神解析一下，谢谢

代码如下

var http = require('http');

var url = require('url');

var util = require('util');

http.createServer(function (req, res) {

res.writeHead(200, {

        "Content-Type": "text/html;charset=utf-8"

    });

    res.end("OK");

    var mysql = require('mysql');

    var connection = mysql.createConnection({

        host: 'localhost',

        user: 'root',

        password: '123456',

        database: 'myData'

    });

	connection.connect();

	connection.query('SELECT * from test', function (err, rows, fields) {

        if (err) {

            console.log(err);

            return;

        };

        var test = rows[0]; //读取num

        var num = test.num - 1;

        var id = test.id;

        connection.query("update test set num=" + num + ",`desc`='" + dateFormat(new Date()) + "'", function (err, res) {

            if (!err) {

                var insert = "insert into testlog(testid,num,`desc`) values ('" + id + "','" + num + "','" + dateFormat(new Date()) + "')";

                connection.query(insert, function (err, res) {

                    if (!err) {

                        connection.end();

                        console.log("update sucess!");

                    } else {

                console.log(err);

                    }

                });

            } else {

                connection.end();

                console.log(err);

               }

        });

    });

    function dateFormat(date) {

        var fmt = "yyyy-MM-dd hh:mm:ss:SS";

        var o = {

            "M+": date.getMonth() + 1,                 //??

            "d+": date.getDate(),                    //?

            "h+": date.getHours(),                   //С?

            "m+": date.getMinutes(),                 //?

            "s+": date.getSeconds(),                 //?

            "q+": Math.floor((date.getMonth() + 3) / 3), //??

            "S+": date.getMilliseconds()             //?ī

        };

        if (/(y+)/.test(fmt)) {

            fmt = fmt.replace(RegExp.$1, (date.getFullYear() + "").substr(4 - RegExp.$1.length));

        }

        for (var k in o) {

            if (new RegExp("(" + k + ")").test(fmt)) {

                fmt = fmt.replace(RegExp.$1, (RegExp.$1.length == 1) ? (o[k]) : (("00" + o[k]).substr(("" + o[k]).length)));

            }

        }

        return fmt;

    }

 }).listen(3000);