php - 尝试检查具有相同值的电子邮件是否已存在

Question

我试图在将数据插入数据库之前检查电子邮件是否已存在于数据库中。

这是我的代码:

<?php
    $servername = "servername";
    $username = "username";
    $password = "password";
    $dbname = "dbname";

    $Mail = $_POST['email'];

    // Create connection
    $conn = new mysqli($servername, $username, $password, $dbname);

    // Check connection
    if ($conn->connect_error) {
    die("Connection failed: " . $conn->connect_error);
    }

    //Inputed in E-Mail Field
    $Mail = $_POST['email'];

    $SearchEmail = $conn->query("SELECT (Mail) FROM betakey WHERE Mail = '$Mail'");

    if ($SearchEmail->num_rows > 0) {
        print "That Email is already registered for the closed alpha";
    }
    else {
        $conn->query("INSERT INTO betakey VALUES ('$Mail')");
    }

    $conn->close();
    ?> 

当我访问该页面时，它不会给我任何错误，但它也不会回显该页面存在或在不存在时插入数据。

Answer 1

问题出在您的插入查询中。插入查询的结构始终如下所示。

INSERT INTO 表名(列 1、列 2、列 3，...)值(值 1、值 2、值 3，...)请参阅:http://www.w3schools.com/php/php_mysql_insert.asp

将此应用到您的代码中，会产生以下结果。

<?php
$servername = "servername";
$username = "username";
$password = "password";
$dbname = "dbname";

$Mail = $_POST['email'];

// Create connection
$conn = new mysqli($servername, $username, $password, $dbname);

// Check connection
if ($conn->connect_error) {
die("Connection failed: " . $conn->connect_error);
}

//Inputed in E-Mail Field
$Mail = $_POST['email'];

$SearchEmail = $conn->query("SELECT count(Mail) FROM betakey WHERE Mail = '$Mail'");

if ($SearchEmail->num_rows > 0) {
    print "That Email is already registered for the closed alpha";
}
else {
    $conn->query("INSERT INTO betakey (Mail) VALUES ('$Mail')");
}

$conn->close();
?> 

我建议你去掉两个'$Mail = $_POST['email'];'之一，因为以同样的方式声明一个变量两次是没有用的。