使用PHP或SQL获取具有选定字段值的两个mysql表中的不同元素

<?php
// 连接到MySQL数据库
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "database";
$conn = new mysqli($servername, $username, $password, $dbname);

// 检查连接是否成功
if ($conn->connect_error) {
    die("连接失败: " . $conn->connect_error);
}

// 编写SQL查询语句
$sql = "SELECT field FROM table1
        UNION
        SELECT field FROM table2";

// 执行查询
$result = $conn->query($sql);

// 处理查询结果
$elements = array();
if ($result->num_rows > 0) {
    while ($row = $result->fetch_assoc()) {
        $elements[] = $row["field"];
    }
}

// 关闭数据库连接
$conn->close();

// 比较两个数组，找出不同的元素
$table1_elements = array("element1", "element2", "element3");
$different_elements = array_diff($table1_elements, $elements);

// 输出结果
echo "不同的元素：";
foreach ($different_elements as $element) {
    echo $element . ", ";
}
?>