HIVE 高级应用(一)--COUNT 高级用法(条件过滤等)

在HIVE中，除了COUNT(*)外，COUNT还可以有很多高级用法。

SELECT
    type
  , count(*)
  , count(DISTINCT u)
  , count(CASE WHEN plat=1 THEN u ELSE NULL END)
  , count(DISTINCT CASE WHEN plat=1 THEN u ELSE NULL END)
  , count(CASE WHEN (type=2 OR type=6) THEN u ELSE NULL END)
  , count(DISTINCT CASE WHEN (type=2 OR type=6) THEN u ELSE NULL END)
FROM
    t
WHERE
    dt in ("2018-05-20", "2018-05-21")
GROUP BY
    type
ORDER BY
    type
;

例如根据消费记录要求计算三餐消费次数

 select xh,jyrq,
 COUNT(distinct(
 case when xfzl ='其他' then null  
 else  concat(jyrq,xfzl) end) ) 
 from (select    xh,jyrq,
 case when hour(jysj) >= 6 and hour(jysj)<10 then '早餐'  
 when hour(jysj) >= 10 and hour(jysj)<16 then '午餐' 
 when hour(jysj) >= 16 and hour(jysj)<22 then '晚餐' 
 else '其他' end as xfzl 
 from gdm.gdm_ykt_jy_log  
 order by xh,jyrq ) t 
 group by xh,jyrq;