PHP MySQL循环遍历各行，并在日期更改时打印日期

$servername = "数据库服务器地址";
$username = "用户名";
$password = "密码";
$dbname = "数据库名";

// 创建连接
$conn = new mysqli($servername, $username, $password, $dbname);

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

$sql = "SELECT * FROM 表名 ORDER BY 日期字段";
$result = $conn->query($sql);

if ($result->num_rows > 0) {
    // 循环遍历每一行数据
    while($row = $result->fetch_assoc()) {
        // 获取日期字段的值
        $date = $row["日期字段"];

        // 打印日期
        echo $date . "<br>";
    }
} else {
    echo "没有数据";
}

$previousDate = null;

if ($result->num_rows > 0) {
    while($row = $result->fetch_assoc()) {
        $date = $row["日期字段"];

        // 判断日期是否更改
        if ($date != $previousDate) {
            echo $date . "<br>";
        }

        // 更新previousDate变量
        $previousDate = $date;
    }
} else {
    echo "没有数据";
}

$conn->close();