获取警告消息mysqli_query期望参数1为mysqli，null给定

Question

我不断从我的代码

中收到此错误

Warning: mysqli_query() expects parameter 1 to be mysqli, null given in C:\xampp\htdocs\citizenssuites\site\pages\reservations.php on line 26

Warning: mysqli_error() expects parameter 1 to be mysqli, null given in C:\xampp\htdocs\citizenssuites\site\pages\reservations.php on line 26
Error querying database the first time

这是我的代码：

$query = "SELECT * FROM reservations, rooms, room_type";
$query .= " WHERE reservations.room_id=rooms.room_id";
$query .= " AND rooms.room_type_id=room_type.room_type_id";
$query .= " AND reservations.arrival < ".$arrival;
$query .= " AND reservations.departure > ".$departure;
$query .= " ORDER BY room_type.room_type_id";
$result = mysqli_query ($connection, $query) or die ('Error querying database the first time' . mysqli_error($connection));

我做错了什么？

Answer 1

您没有先调用mysqli_connect，否则失败。首先将$connection设置为有效连接：

$connection = mysqli_connect("hostname", "username", "password");
if (mysqli_connect_error()) {
    die("Error: " . mysqli_connect_error());
}
$result = mysqli_query($connection, ...);

Answer 2

函数mysqli_connection失败（或者您忘记调用它？）并返回null，当您稍后尝试$connection使用mysqli_query时会返回错误。