javascript - 变量不保留值

Question

我尝试将变量设置为从查询获得的结果，但该变量不保留该值。

var queryString = "SELECT price FROM menu_items WHERE id = " + 
    req.query.items + ";";
mysql.pool.query(queryString, function(err, rows, fields){
    if (err){
        next(err);
        return;
    }
    itemPrice = rows[0].price;
    console.log("item price is2: " + itemPrice);
});

console.log("item price is: " + itemPrice);

我希望它打印“item Price is2:10.99”，然后“item Price is 10.99”，但它打印item Price is undefined 然后商品价格为2:10.99

Answer 1

var queryString = "SELECT price FROM menu_items WHERE id = " + 
    req.query.items + ";";
mysql.pool.query(queryString, function(err, rows, fields){
    if (err){
        next(err);
        return;
    }
    itemPrice = rows[0].price;
    console.log("item price is2: " + itemPrice);
    console.log("item price is: " + itemPrice);
});