sql 查询每隔3天的量

思路：根据日期yyyy-MM-dd mm:HH:ss 格式，天数dd/3 归于dd/3×3 ，00，01，02 为00,进行分组统计。

sql如下：

select substr(FROM_UNIXTIME((curtime)/1000),1,14) ||
                                 case when substr(FROM_UNIXTIME((curtime)/1000),15,2)/3*3 <10 then '0'||substr(FROM_UNIXTIME((curtime)/1000),15,2)/3*3               
                                 else substr(FROM_UNIXTIME((curtime)/1000),15,2)/3*3 end
                                                  ||'00' as dt,
       count(1)
       FROM TXN
       WHERE curtime > UNIX_TIMESTAMP('2018/10/11 14:22:51')
       GROUP BY dt;