在尝试获取MySQL数据时，php返回空的GET数组

I am trying to make a php REST API for my mobile backend to interact with a MySQL database. I have written out the following code to try and retrieve data from a MySQL query:

我正在尝试为我的移动后端制作一个php REST API，以便与MySQL数据库进行交互。我已经写出以下代码来尝试从MySQL查询中检索数据：

<?php include "FILE WITH DB_INFO"; ?>
    <html>
    <body>
    <h1>Testing page</h1>
<?php

$connection = mysqli_connect(DB_SERVER, DB_USERNAME, DB_PASSWORD);

if (mysqli_connect_errno()) echo "Failed to connect to MySQL" . mysqli_connect_error();


$database = mysqli_select_db($connection, DB_DATABASE);

if (strlen($username_query)) {
    doesUsernameExist($connection, $username_query);
}

doesUsernameExist($connection, $username_query);

$username_query = $_GET['usernameToQuery'];

echo($_GET['usernameToQuery']);


function doesUsernameExist($connection, $username) {
    $u = mysqli_real_escape_string($connection, $username);

    $query = "SELECT username from users WHERE username = ('$u');";


if (!mysqli_query($connection, $query)) {
    $response = array("success" => false, "message" => mysqli_error($connection), "sqlerrno" => mysqli_errno($connection), "sqlstate" => mysqli_sqlstate($connection));
    echo json_encode($response);
} else {
    $sth = mysqli_query($connection, $query);
    $rows = array();
    while($r = mysqli_fetch_assoc($sth)) {
        $rows[] = $r;
    }
    $response = array("success" => true);
    echo json_encode($rows);
}

}
?>

This is what the actual request looks like: http://my_ec2_instance/DoesUsernameExist.php?usernameToQuery=lmao. This is sent through POSTMAN.

这是实际请求的样子：http：//my_ec2_instance/DoesUsernameExist.php？usernameToQuery = lmao。这是通过POSTMAN发送的。

Because the MySQL database that I am using contains usernames with the value lmao, the php function should return an array that is not empty. But the json_encode($rows); line returns an empty array []. What am I doing wrong.

因为我使用的MySQL数据库包含值为lmao的用户名，所以php函数应该返回一个非空的数组。但是json_encode（$ rows）; line返回一个空数组[]。我究竟做错了什么。

1 个解决方案

#1

It seems you call doUsernameExiste() and just before strlen with a variable $username_query. But you define $username_query only after.

看来你在strlen之前使用变量$ username_query调用doUsernameExiste（）。但是你只能在之后定义$ username_query。

You should first do your affectation. Put this after your line with the mysqli_select_db

你应该先做好准备。把它放在你的mysqli_select_db之后

$username_query = $_GET['usernameToQuery'];

$ username_query = $ _GET ['usernameToQuery'];

#1