Getting a warning message mysqli_query expects parameter 1 to be mysqli, null given

问题

I keep getting this error from my code

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

Here is my code:

$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));

What am I doing wrong?

回答1:

You didn't call mysqli_connect first, or it failed. Set $connection to a valid connection first:

mysqli_report(MYSQLI_REPORT_ERROR | MYSQLI_REPORT_STRICT);
$connection = mysqli_connect("hostname", "username", "password");
$result = mysqli_query($connection, ...);

回答2:

The function mysqli_connection fails (or did you forget calling it?) and returns null which causes the error when you try to use $connection later on with mysqli_query.

来源：https://stackoverflow.com/questions/24859392/getting-a-warning-message-mysqli-query-expects-parameter-1-to-be-mysqli-null-gi