多行数据合并成一行

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需求：在大数据平台maxcompute上统计各个等级对应的人数，字段大致如下

CREATE TABLE `XXXX` (
  `requestid` char(32) DEFAULT NULL,
  `id` char(32) NOT NULL,
  `createtime` varchar(50) DEFAULT NULL COMMENT '创建时间',
  `createdate` varchar(50) DEFAULT NULL COMMENT '创建日期',
  `showdate` varchar(50) NOT NULL DEFAULT '' COMMENT '统计日期',
  `total` int(11) DEFAULT '0' COMMENT '总人数',
  `five_star_num` int(11) DEFAULT '0' COMMENT '五星级人数',
  `four_star_num` int(11) DEFAULT '0' COMMENT '四星级人数',
  `three_star_num` int(11) DEFAULT '0' COMMENT '三星级人数',
  `two_star_num` int(11) DEFAULT '0' COMMENT '二星级人数',
  `one_star_num` int(11) DEFAULT '0' COMMENT '一星级人数',
  `zero_star_num` int(11) DEFAULT '0' COMMENT '零星级人数',
  `new_member` int(11) DEFAULT '0' COMMENT '新增用户数',
  PRIMARY KEY (`showdate`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 ROW_FORMAT=DYNAMIC COMMENT='日活-用户等级变化统计表';

目前面临的问题：各个等级都在一张表中，可以按等级分类查询人数，查询语句如下：

查询出各个等级对应的人数

select user_level,count(id) as count from XXX where register_date<=? group by user_level 

查询结果如下

然而现在只能在大数据平台（maxcompute）编写sql，不能借助任何高级语句（如java），要实现将表内的数据以一行的形式存储到

with a1 as (
    select user_level,count(id) as count from XXXXXXX where register_date<=? group by user_level 
),a4 as(
    select  
        sum(CASE when a1.user_level="0" then a1.count else 0 end) as zero_star_num, 
        sum(CASE when a1.user_level="1" then a1.count else 0 end) as one_star_num, 
        sum(CASE when a1.user_level="2" then a1.count else 0 end) as two_star_num, 
        sum(CASE when a1.user_level="3" then a1.count else 0 end) as three_star_num, 
        sum(CASE when a1.user_level="4" then a1.count else 0 end) as four_star_num,
        sum(CASE when a1.user_level="5" then a1.count else 0 end) as five_star_num from a1 
)
select * from a4

结果如下