SQL语句 分组统计问题

统计各个年龄阶段的人数和性别

select
         ageGroup  as '年龄段'
       , cont(*)   as '人数'
       , sex       as '性别'
from
         (
                select
                       case
                              when age      >=1
                                     and age<=10
                                     then '1-10'
                              when age      >=11
                                     and age<=20
                                     then '11-20'
                              when age      >=21
                                     and age<=30
                                     then '21-30'
                              when age      >=31
                                     and age<=40
                                     then '31-40'
                                     else 'other'
                       end as ageGroup
                     , uname
                     , sex
                from
                       table
         )
         t
group by
         ageGroup
       , sex

postgresql统计

• 统计每小时的数量
  思路: 格式化时间保留到小时,然后使用concat拼接00分00秒

SELECT
         COUNT(id)                                            cnt
       , CONCAT(to_char(create_time,'yyyy-mm-dd hh24'),':00:00') H
FROM
         table a
GROUP BY
                  CONCAT(to_char(create_time,'yyyy-mm-dd hh24'),':00:00')
ORDER BY
         H

• 每隔5秒统计一次
  比如01秒、04秒统一标识为00秒，05、06、09秒统一标识为05秒
  思路: 截取秒最后一位和5进行比较

SELECT
         tmp.newTime
       , tmp.name
       , COUNT(1) totalNum
FROM
         (
                  SELECT
                           t.id
                         , t.name
                         , t.create_time oldTime
                         , -- 原来的时间
                           CASE
                                    WHEN SUBSTR(to_char(t.create_time,'yyyy-mm-dd hh24:mi:ss'),19,1)::integer <5
                                             THEN CONCAT(SUBSTR(to_char(t.create_time,'YYYY-mm-dd hh24:mi:ss'),0,19),'0')
                                             ELSE CONCAT(SUBSTR(to_char(t.create_time,'yyyy-mm-dd hh24:mi:ss'),0,19),'5')
                           END AS newTime -- 时间段伪列
                  FROM
                           table t
                  ORDER BY
                           create_time ASC
         )
         tmp
GROUP BY
         tmp.newTime
       , tmp.name