wpquestions.com, ID = 2790

function room_current_select_location_number_of_racks( $attr ) {

    global $wpdb;

    // Get shortcode parameters :
    // Date Range (by month).  Default: Last Calendar Month
    $date = ( isset( $attr['date'] ) ) ? $attr['date'] : date('m/Y',strtotime("last month"));

    // Room_desc. Default value: ALL Rooms  (if no parameter is provided, it returns all rooms)
    $room_desc = ( isset( $attr['room_desc'] ) ) ? "AND L.room_desc = '" . $attr['room_desc'] . "'" : '';

    //Item_category.  Default value:  ALL Item Categories  (if no parameter is provided, it returns all categories)
    $item_category = ( isset( $attr['item_category'] ) ) ? "AND I.item_category = '" .$attr['item_category']  . "'": '';

    // Set up query and make sure it's always secure (no malformed SQL injection etc...)
    $query = $wpdb->prepare( "
        SELECT
            I.item_desc,
            SUM(T.quantity)

        FROM
            wp_transactions T,
            wp_location L,
            wp_items I

        WHERE
            T.item_id=I.item_id
            AND T.location_id=L.location_id
            $item_category      // 'Red Widgets, Blue Widgets, etc
            $room_desc          //ROOM 4A, ROOM 4B, etc
            AND T.date= '$date' //  03/2011, 05/2011 etc

        GROUP BY
            I.item_desc

        ORDER BY
            I.item_name

    " );

    $r = $wpdb->get_var( $query );

    // next few lines simply print the results of the query on screen, nothing fancy
    echo '<pre>';
    print_r ( $r );
    echo '</pre>';

}

// Register a new shortcode
// Usage :
// [19]
// [19 room_desc="ROOM 4A"]    returns Room 4A, and defaults values:   ALL item_category, date=Last Calendar Month
// [19 item_category="Blue Widgets"]   returns Blue Widgets, and default values:    ALL room_desc, date=Last Calendar Month
//[19 item_category="Green Widgets" date='03/2011'] returns Green Widgets, for March, 2011  and default value:  ALL room_desc

add_shortcode( '19', 'room_current_select_location_number_of_racks' );