PHP:在datetime之间搜索MYSQL数据库，但只使用日期？

<?php
// 连接数据库
$servername = "数据库服务器地址";
$username = "数据库用户名";
$password = "数据库密码";
$dbname = "数据库名";

$conn = new mysqli($servername, $username, $password, $dbname);
if ($conn->connect_error) {
    die("连接失败: " . $conn->connect_error);
}

// 搜索日期范围
$start_date = '2022-01-01';
$end_date = '2022-01-31';

// 构建查询语句
$sql = "SELECT * FROM 表名 WHERE DATE(datetime字段名) BETWEEN '$start_date' AND '$end_date'";

$result = $conn->query($sql);

if ($result->num_rows > 0) {
    // 输出数据
    while($row = $result->fetch_assoc()) {
        echo "字段1: " . $row["字段1"]. " - 字段2: " . $row["字段2"]. "<br>";
    }
} else {
    echo "没有结果";
}

$conn->close();
?>