foreach数组保持返回第一个值？

First of all I don't know php and I certainly don't know sql or how wordpress interacts with it, but I have to use php etc so here I am. So please try to explain things clearly and simply.

I have added three values to my sql wordpress tables. Two values share the same room_id (1) and the third has a value of (2). They each have a different start and end date in the table. I am trying to loop through each room_id first, checking the dates, before moving to the next room. I have more code with this function but essentially my problem is that I only seem to be printing out the first value of the array with each iteration. Here is the code:

<?php 
/*Plugin Name: HotelMania Functions*/
function checkRoom() {
    global $wpdb;
    $query = "SELECT * FROM hm_booking ORDER BY room_id DESC";
    $rooms = $wpdb->get_results($query);    
    foreach ($rooms as $room) {
       $test= $wpdb->get_var("SELECT room_id FROM hm_booking");
       echo $test;
}    
}
add_shortcode('TEST', 'checkRoom');
?>

When I try to test the value either using room_id or start_date I keep getting hte first value in the table. But I think my sql is right because it is working in the database. Please can someone help I have read around and can't seem to figure out what I am doing wrong.

Thanks in advance.

Once you got $rooms from get_results, you don't need to run another query with get_var.

For example, to get the room_id and place it into $test, instead of

$test= $wpdb->get_var("SELECT room_id FROM hm_booking");

do

$test = $room->room_id;

The SQL statement you're using "SELECT room_id FROM hm_booking" along with get_var() will return the same value no matter what. The codex mentions that:

The get_var function returns a single variable from the database.

Assuming the hm_booking table contains multiple rows, then the SQL statement you're running will return multiple rows of just the room_id column in your table, and the get_var() function will only return the first row of the room_id column.

Also, consider taking advantage of get_results(). Your first SQL query may already be storing everything you need. The $rooms variable is an object containing all the rows and columns from your SELECT query:

$query = "SELECT * FROM hm_booking ORDER BY room_id DESC";
$rooms = $wpdb->get_results($query);    
foreach ($rooms as $room) {
    echo 'Room ID:' . $room->room_id; // $room object represents a single row
}