PHP/MySql 错误:字段不存在，但确实存在

我不知道为什么在我的进程.php页面上出现此错误：

Connected successfully
Could not run query: Table 'members_db.members where 'email' = '123456789'' doesn't exist 
Invalid query: Duplicate entry '123456789' for key 'email'

没有多大意义，因为它似乎在错误消息中自相矛盾。

这是我的过程.php：

<?php
session_start();
$con = mysql_connect('localhost', 'root', ''); 
if (!$con) { 
    die('Could not connect: ' . mysql_error()); 
} 
echo 'Connected successfully<br />'; 
// make members the current db
$db_selected = mysql_select_db('members_db', $con);
if (!$db_selected) {
    die ('Can''t use members database : ' . mysql_error());
}
$hash_password = md5($_POST['password']);
$email = $_POST['email'];
$result = mysql_query("SELECT email,password FROM `members WHERE 'email' = '$email'");
if (!$result) {
    echo 'Could not run query: ' . mysql_error();
    $query = "INSERT INTO members (email, password)
    VALUES('".$_POST['email']."','".$hash_password."')";
    // Perform Query
    $result2 = mysql_query($query);
    // Check result
    // This shows the actual query sent to MySQL, and the error. Useful for debugging.
    if (!$result2) {
        $message  = 'Invalid query: ' . mysql_error() . "'n";
        //$message .= 'Whole query: ' . $query;
        die($message);
    }   
$_SESSION['email']=$_POST['email'];
$_SESSION['password']=$hash_password;
$_SESSION['loggedin']="YES";
$url = "Location: /welcome.php";
header($url);
}
$_SESSION['email']=$_POST['email'];
$_SESSION['password']=$hash_password;
$url = "Location: /checklogin.php";
header($url);
?> 

这可能是一个愚蠢的错误，因为我在做这个项目时正在学习。感谢您的任何帮助！