格式化 SQL 语句以读取 PHP 内部

Question

以下代码在 phpmyadmin SQL 窗口中完美运行

"SET @sql = (SELECT GROUP_CONCAT(DISTINCT
               CONCAT(
               "SUM(CASE WHEN `room_id` = '", rr.room_id, "' THEN `roomrate_value` ELSE 0 END) AS `", `room_name`, "`"
                )
               )
            FROM tbl_roomrates rr
            INNER JOIN tbl_rooms ro ON ro.room_id = rr.room_id
            );
SET @sql = CONCAT("SELECT rate_name AS `RATE CODE`, ", @sql, " 
                  FROM tbl_roomrates rr
                  INNER JOIN tbl_rates ra ON ra.rate_id = rr.rate_id
                  GROUP BY rr.rate_id");
PREPARE stmt FROM @sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;"

但是，当插入 PHP 时，它会抛出一个错误：

语法错误，意外的 SUM (T_String)

请帮忙