php - 准备好的语句检查行是否存在

Question

我是 Php 中准备好的语句的新手，并且想知道您最好如何检查一行是否已经存在，因为我在这个阶段似乎感到困惑:

<?php 
include '../config.php'; 

$stmt = $conn->prepare("INSERT INTO users (email, password) VALUES (?, ?)");
$stmt->bind_param("ss", $email, $password);

if(mysqli_num_rows($stmt) > 0) {
    $email = $_POST['email'];
    $password = $_POST['password'];
    $stmt->execute();
    header('Location: ../login.php');   
} else {
    echo 'user already exists';
}
$stmt->close();
$conn->close();
?>

上面返回了 else 语句，如果我将它们切换过来，它会再次插入使用 else 语句并插入记录但仍然不检查。

**更新**

这是我更新后的代码，供您在下面的帮助后查看。

<?php 
include '../config.php'; 

ini_set('display_errors', 1); ini_set('display_startup_errors', 1); error_reporting(E_ALL);

$email = $_POST['email'];
$password = $_POST['password'];

$stmt_check = $conn->prepare("SELECT * FROM users WHERE email =?");
$stmt_check->bind_param("s", $email);
$stmt_check->execute();
if($stmt_check->num_rows > 0) {
    echo 'user already exists';
} else {
    $stmt = $conn->prepare("INSERT INTO users (email, password) VALUES (?, ?)");
    $stmt->bind_param("ss", $email, $password);
    $stmt->execute();
    // header('Location: ../login.php');
}    
$stmt->close();
$conn->close();
?>

Answer 1

mysqli_num_rows 适用于 SELECT 语句。

$stmt_check = $conn->prepare("SELECT * FROM users WHERE email =? AND password =?");
$stmt_check->bind_param("ss", $email, $password);
$stmt_check->execute();
if(mysqli_num_rows($stmt_check) > 0)

更新代码

<?php 

include '../config.php'; 

$email = $_POST['email'];
$password = $_POST['password'];

$stmt_check = $conn->prepare("SELECT * FROM users WHERE email =? AND password =?");
$stmt_check->bind_param("ss", $email, $password);
$stmt_check->execute();
if($stmt_check->num_rows > 0){
  echo 'user already exists';
} else {
  $stmt = $conn->prepare("INSERT INTO users (email, password) VALUES (?, ?)");
  $stmt->bind_param("ss", $email, $password);
  $stmt->execute();
  header('Location: ../login.php');
}

$stmt->close();
$conn->close();
?>

快速链接

• mysqli_num_rows
• mysql_num_rows

哪个州，

This command is only valid for statements like SELECT or SHOW that return an actual result set. To retrieve the number of rows affected by a INSERT, UPDATE, REPLACE or DELETE query, use mysql_affected_rows().

编辑 1

改变

if(mysqli_num_rows($stmt_check) > 0){

到

if($stmt_check->num_rows > 0){

参见 PHP mysqli_num_rows() Function 的Example2