Hive分析、窗口函数

LAG(col,n,default) 用于统计窗口内往上第n行值

第一个参数为列名，第二个参数为往上第n行（可选，默认为1），第三个参数为默认值（当往上第n行为NULL时候，取默认值，如不指定，则为NULL）

LEAD与LAG相反 ，LEAD(col,n,DEFAULT) 用于统计窗口内往下第n行值

第一个参数为列名，第二个参数为往下第n行（可选，默认为1），第三个参数为默认值（当往下第n行为NULL时候，取默认值，如不指定，则为NULL）

例子：获取用户这次下单与下次会话的时间，统计时间差

select session_id, user_id, session_create_time, 
LEAD(session_create_time,1) over (order by session_create_time asc) as next_row 
from dwb.dwb_pulsar_c_inappropriate_hour
where user_id = '1105835577';

获取上一次与这一次下单的间隔时间

select session_id, user_id, session_create_time, 
LEAD(session_create_time,1) over (order by session_create_time asc) as next_row,
datediff(LEAD(session_create_time, 1) over(order by session_create_time asc),session_create_time) as diff_days
from dwb.dwb_pulsar_c_inappropriate_hour
where user_id = '1105835577';

SELECt
   user_id, session_id, session_create_time,
   ROW_NUMBER() OVER(PARTITION BY user_id ORDER BY session_create_time DESC) AS rank
FROM dwb.dwb_pulsar_c_inappropriate_hour
ORDER BY user_id;

其他方式实现

方法一： ROW_NUMBER() OVER(PARTITION BY

SELECt t.user_id, t.session_id, t.session_create_time
FROM( 
SELECt
   user_id, session_id, session_create_time,
   ROW_NUMBER() OVER(PARTITION BY user_id ORDER BY session_create_time DESC) AS rank
FROM dwb.dwb_pulsar_c_inappropriate_hour
)t
WHERe t.rank = 1 ORDER BY t.user_id;

 方法二： rowNumberInAllBlocks()函数

SELECt t.user_id, t.session_id, t.session_create_time
FROM( 
SELECt
    user_id, session_id, session_create_time,
    rowNumberInAllBlocks() AS rank
FROM dwb.dwb_pulsar_c_inappropriate_hour
)t
LIMIT 1 BY user_id;

方法三：max()函数

SELECt t.user_id, t.session_id, t.session_create_time
FROM
dwb.dwb_pulsar_c_inappropriate_hour a
left join ( 
SELECt
    user_id, max(session_create_time) session_create_time
FROM dwb.dwb_pulsar_c_inappropriate_hour
GROUP BY user_id
)t
on a.user_id = t.user_id 
and a.session_create_time = t.session_create_time;