connection.query返回数据

Question

var mysql = require('mysql');

var connection = mysql.createConnection(
    {
        host: 'localhost',
        user: 'root',
        password: 'root',
        port: 3306,
        database: 'covid19'
    });

connection.connect();

var sql = `select * from all_information`;

connection.query(sql,(err, result) => {
    if(err){
            console.error('error',err)
            return;
        }

    a = result[0];

    })

connection.end()

console.log(a)

打印a发现是defind，如何才能把result的值赋值给a并打印出来啊。

Answer 1

你先改成这样验证一下

var mysql = require('mysql');
 
var connection = mysql.createConnection(
    {
        host: 'localhost',
        user: 'root',
        password: 'root',
        port: 3306,
        database: 'covid19'
    });
 
connection.connect();
 
var sql = `SELECT 1 + 1 AS solution`;
 
connection.query(sql,(err, result) => {
    if(err){
            console.error('error',err)
            return;
        }
 
    a = result[0];
 console.log(a)
    })
 
connection.end()