MySql grouping and randomly getting one piece of data from each group

CREATE TABLE `xdx_test` (
 `id` int(11) NOT NULL,
 `name` varchar(255) DEFAULT NULL,
 `class` varchar(255) DEFAULT NULL,
 PRIMARY KEY (`id`)
)ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;

INSERT INTO xdx_test VALUES (1, '张三-1','1');
INSERT INTO xdx_test VALUES (2, 'Li Si-1','1');
INSERT INTO xdx_test VALUES (3, '王五-1','1');
INSERT INTO xdx_test VALUES (4, '张三-2','2');
INSERT INTO xdx_test VALUES (5, 'Li Si-2','2');
INSERT INTO xdx_test VALUES (6, '王五-2','2');
INSERT INTO xdx_test VALUES (7, '张三-3','3');
INSERT INTO xdx_test VALUES (8, 'Li Si-3','3');
INSERT INTO xdx_test VALUES (9, '王五-3','3');

SELECT * FROM 
 (SELECT * FROM xdx_test ORDER BY RAND()) a
GROUP BY a.class

DROP PROCEDURE IF EXISTS `evaluate_Check_procedure`;
DELIMITER ;;
CREATE DEFINER=`root`@`%` PROCEDURE `evaluate_Check_procedure`(IN startTime datetime, IN endTime datetime,IN checkNum INT,IN evaInterface VARCHAR(36))
BEGIN

create temporary table if not exists xdr_authen_tmp ( 
 `ID` bigint(20) NOT NULL AUTO_INCREMENT COMMENT 'Serial number',
 `LENGTH` int(5) DEFAULT NULL COMMENT 'Number of bytes',
 `INTERFACE` int(3) NOT NULL COMMENT 'Interface',
 `XDR_ID` varchar(32) NOT NULL COMMENT 'XDR ID',
 `MSISDN` varchar(32) DEFAULT NULL COMMENT 'User number',
 `PROCEDURE_START_TIME` datetime NOT NULL DEFAULT '0000-00-00 00:00:00' COMMENT 'Start time',
 `PROCEDURE_END_TIME` datetime DEFAULT NULL COMMENT 'End time',
 `SOURCE_NE_IP` varchar(39) DEFAULT NULL COMMENT 'Source NE IP',
 `SOURCE_NE_PORT` int(5) DEFAULT NULL COMMENT 'Source NE port',
 `DESTINATION_NE_IP` varchar(39) DEFAULT NULL COMMENT 'Destination network element IP',
 `DESTINATION_NE_PORT` int(5) DEFAULT NULL COMMENT 'Destination network element port',
 `INSERT_DATE` datetime DEFAULT NULL COMMENT 'Insert time',
 `EXTEND1` varchar(50) DEFAULT NULL COMMENT 'Extension 1',
 `EXTEND2` varchar(50) DEFAULT NULL COMMENT 'Extension 2',
 `EXTEND3` varchar(50) DEFAULT NULL COMMENT 'Extension 3',
 `EXTEND4` varchar(50) DEFAULT NULL COMMENT 'Extension 4',
 `EXTEND5` varchar(50) DEFAULT NULL COMMENT 'Extension 5',
 PRIMARY KEY (`ID`,`PROCEDURE_START_TIME`),
 KEY `index_procedure_start_time` (`PROCEDURE_START_TIME`),
 KEY `index_source_dest_ip` (`SOURCE_NE_IP`,`DESTINATION_NE_IP`),
 KEY `index_xdr_id` (`XDR_ID`) 
)ENGINE = InnoDB DEFAULT CHARSET = utf8;

BEGIN
DECLARE j INT;
DECLARE i INT;

DECLARE CONTINUE HANDLER FOR NOT FOUND SET i = 1;

SET j = 0;
WHILE j < checkNum DO 
 set @sqlexi = concat( ' SELECT t1.ID,t1.LENGTH,t1.LOCAL_PROVINCE,t1.LOCAL_CITY,t1.OWNER_PROVINCE,t1.OWNER_CITY,t1.ROAMING_TYPE,t1.INTERFACE,t1.XDR_ID,t1.RAT,t1.IMSI,t1.IMEI,t1.MSISDN,t1.PROCEDURE_START_TIME,t1.PROCEDURE_END_TIME,t1.TRANSACTION_TYPE,t1.TRANSACTION_STATUS,t1.SOURCE_NE_IP,t1.SOURCE_NE_PORT,t1.DESTINATION_NE_IP,t1.DESTINATION_NE_PORT,t1.RESULT_CODE,t1.EXPERIMENTAL_RESULT_CODE,t1.ORIGIN_REALM,t1.DESTINATION_REALM,t1.ORIGIN_HOST,t1.DESTINATION_HOST,t1.INSERT_DATE',
    ' into @ID,@LENGTH,@LOCAL_PROVINCE,@LOCAL_CITY,@OWNER_PROVINCE,@OWNER_CITY,@ROAMING_TYPE,@INTERFACE,@XDR_ID,@RAT,@IMSI,@IMEI,@MSISDN,@PROCEDURE_START_TIME,@PROCEDURE_END_TIME,@TRANSACTION_TYPE,@TRANSACTION_STATUS,@SOURCE_NE_IP,@SOURCE_NE_PORT,@DESTINATION_NE_IP,@DESTINATION_NE_PORT,@RESULT_CODE,@EXPERIMENTAL_RESULT_CODE,@ORIGIN_REALM,@DESTINATION_REALM,@ORIGIN_HOST,@DESTINATION_HOST,@INSERT_DATE ',
    ' FROM xdr_authen t1 JOIN (SELECT ROUND(RAND() * ((SELECT MAX(id) FROM xdr_authen)-(SELECT MIN(id) FROM xdr_authen)) + (SELECT MIN(id) FROM xdr_authen)) AS id) t2',
    ' WHERE t1.PROCEDURE_START_TIME >= "',startTime,'"',
       ' AND t1.PROCEDURE_START_TIME < "',endTime,'"',' AND t1.INTERFACE IN (',evaInterface,')',
       ' and t1.id >= t2.id limit 1');
 PREPARE sqlexi FROM @sqlexi;
 EXECUTE sqlexi;
 DEALLOCATE PREPARE sqlexi;

 select count(1) into @num from xdr_authen_tmp where id = @ID;
 
 if @num > 0 or i=1 then 
  SET j = j;
 ELSE
  insert into xdr_authen_tmp(ID,LENGTH,LOCAL_PROVINCE,LOCAL_CITY,OWNER_PROVINCE,OWNER_CITY,ROAMING_TYPE,INTERFACE,XDR_ID,RAT,IMSI,IMEI,MSISDN,PROCEDURE_START_TIME,PROCEDURE_END_TIME,TRANSACTION_TYPE,TRANSACTION_STATUS,SOURCE_NE_IP,SOURCE_NE_PORT,DESTINATION_NE_IP,DESTINATION_NE_PORT,RESULT_CODE,EXPERIMENTAL_RESULT_CODE,ORIGIN_REALM,DESTINATION_REALM,ORIGIN_HOST,DESTINATION_HOST,INSERT_DATE)
  VALUES(@ID,@LENGTH,@LOCAL_PROVINCE,@LOCAL_CITY,@OWNER_PROVINCE,@OWNER_CITY,@ROAMING_TYPE,@INTERFACE,@XDR_ID,@RAT,@IMSI,@IMEI,@MSISDN,@PROCEDURE_START_TIME,@PROCEDURE_END_TIME,@TRANSACTION_TYPE,@TRANSACTION_STATUS,@SOURCE_NE_IP,@SOURCE_NE_PORT,@DESTINATION_NE_IP,@DESTINATION_NE_PORT,@RESULT_CODE,@EXPERIMENTAL_RESULT_CODE,@ORIGIN_REALM,@DESTINATION_REALM,@ORIGIN_HOST,@DESTINATION_HOST,@INSERT_DATE);
 
  SET j = j + 1;
 end if; 
 SET i=0;

END WHILE; 

select ID,LENGTH,LOCAL_PROVINCE,LOCAL_CITY,OWNER_PROVINCE,OWNER_CITY,ROAMING_TYPE,INTERFACE,XDR_ID,RAT,IMSI,IMEI,MSISDN,PROCEDURE_START_TIME,PROCEDURE_END_TIME,TRANSACTION_TYPE,TRANSACTION_STATUS,SOURCE_NE_IP,SOURCE_NE_PORT,DESTINATION_NE_IP,DESTINATION_NE_PORT,RESULT_CODE,EXPERIMENTAL_RESULT_CODE,ORIGIN_REALM,DESTINATION_REALM,ORIGIN_HOST,DESTINATION_HOST,INSERT_DATE from xdr_authen_tmp;

END;
truncate TABLE xdr_authen_tmp;

END
;;
DELIMITER ;