Hive分析窗口函数(四)LAG,LEAD,FIRST_VALUE,LAST_VALUE

1.LAG功能是什么？ 2.LEAD与LAG功能有什么相的地方那个？ 3.FIRST_VALUE与LAST_VALUE分别完成什么功能？ 继续学习这四个分析函数。注意： 这几个函数不支持WINDOW子句。 Hive版本为 apache-hive-0.13.1 数据准备： 水电费 cookie1,2015-04-10 10:00:02,url2

1.LAG功能是什么？
2.LEAD与LAG功能有什么相似的地方那个？

3.FIRST_VALUE与LAST_VALUE分别完成什么功能？

继续学习这四个分析函数。 注意： 这几个函数不支持WINDOW子句。 Hive版本为 apache-hive-0.13.1 数据准备：

水电费

    cookie1,2015-04-10 10:00:02,url2
    cookie1,2015-04-10 10:00:00,url1
    cookie1,2015-04-10 10:03:04,1url3
    cookie1,2015-04-10 10:50:05,url6
    cookie1,2015-04-10 11:00:00,url7
    cookie1,2015-04-10 10:10:00,url4
    cookie1,2015-04-10 10:50:01,url5
    cookie2,2015-04-10 10:00:02,url22
    cookie2,2015-04-10 10:00:00,url11
    cookie2,2015-04-10 10:03:04,1url33
    cookie2,2015-04-10 10:50:05,url66
    cookie2,2015-04-10 11:00:00,url77
    cookie2,2015-04-10 10:10:00,url44
    cookie2,2015-04-10 10:50:01,url55

    CREATE EXTERNAL TABLE lxw1234 (
    cookieid string,
    createtime string,  --页面访问时间
    url STRING       --被访问页面
    ) ROW FORMAT DELIMITED
    FIELDS TERMINATED BY ','
    stored as textfile location '/tmp/lxw11/';


    hive> select * from lxw1234;
    OK
    cookie1 2015-04-10 10:00:02     url2
    cookie1 2015-04-10 10:00:00     url1
    cookie1 2015-04-10 10:03:04     1url3
    cookie1 2015-04-10 10:50:05     url6
    cookie1 2015-04-10 11:00:00     url7
    cookie1 2015-04-10 10:10:00     url4
    cookie1 2015-04-10 10:50:01     url5
    cookie2 2015-04-10 10:00:02     url22
    cookie2 2015-04-10 10:00:00     url11
    cookie2 2015-04-10 10:03:04     1url33
    cookie2 2015-04-10 10:50:05     url66
    cookie2 2015-04-10 11:00:00     url77
    cookie2 2015-04-10 10:10:00     url44
    cookie2 2015-04-10 10:50:01     url55

LAG

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）

    SELECT cookieid,
    createtime,
    url,
    ROW_NUMBER() OVER(PARTITION BY cookieid ORDER BY createtime) AS rn,
    LAG(createtime,1,'1970-01-01 00:00:00') OVER(PARTITION BY cookieid ORDER BY createtime) AS last_1_time,
    LAG(createtime,2) OVER(PARTITION BY cookieid ORDER BY createtime) AS last_2_time
    FROM lxw1234;


    cookieid createtime             url    rn       last_1_time             last_2_time
    -------------------------------------------------------------------------------------------
    cookie1 2015-04-10 10:00:00     url1    1       1970-01-01 00:00:00     NULL
    cookie1 2015-04-10 10:00:02     url2    2       2015-04-10 10:00:00     NULL
    cookie1 2015-04-10 10:03:04     1url3   3       2015-04-10 10:00:02     2015-04-10 10:00:00
    cookie1 2015-04-10 10:10:00     url4    4       2015-04-10 10:03:04     2015-04-10 10:00:02
    cookie1 2015-04-10 10:50:01     url5    5       2015-04-10 10:10:00     2015-04-10 10:03:04
    cookie1 2015-04-10 10:50:05     url6    6       2015-04-10 10:50:01     2015-04-10 10:10:00
    cookie1 2015-04-10 11:00:00     url7    7       2015-04-10 10:50:05     2015-04-10 10:50:01
    cookie2 2015-04-10 10:00:00     url11   1       1970-01-01 00:00:00     NULL
    cookie2 2015-04-10 10:00:02     url22   2       2015-04-10 10:00:00     NULL
    cookie2 2015-04-10 10:03:04     1url33  3       2015-04-10 10:00:02     2015-04-10 10:00:00
    cookie2 2015-04-10 10:10:00     url44   4       2015-04-10 10:03:04     2015-04-10 10:00:02
    cookie2 2015-04-10 10:50:01     url55   5       2015-04-10 10:10:00     2015-04-10 10:03:04
    cookie2 2015-04-10 10:50:05     url66   6       2015-04-10 10:50:01     2015-04-10 10:10:00
    cookie2 2015-04-10 11:00:00     url77   7       2015-04-10 10:50:05     2015-04-10 10:50:01


    last_1_time: 指定了往上第1行的值，default为'1970-01-01 00:00:00'  
                 cookie1第一行，往上1行为NULL,因此取默认值 1970-01-01 00:00:00
                 cookie1第三行，往上1行值为第二行值，2015-04-10 10:00:02
                 cookie1第六行，往上1行值为第五行值，2015-04-10 10:50:01
    last_2_time: 指定了往上第2行的值，为指定默认值
                                                     cookie1第一行，往上2行为NULL
                                                     cookie1第二行，往上2行为NULL
                                                     cookie1第四行，往上2行为第二行值，2015-04-10 10:00:02
                                                     cookie1第七行，往上2行为第五行值，2015-04-10 10:50:01

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）

    SELECT cookieid,
    createtime,
    url,
    ROW_NUMBER() OVER(PARTITION BY cookieid ORDER BY createtime) AS rn,
    LEAD(createtime,1,'1970-01-01 00:00:00') OVER(PARTITION BY cookieid ORDER BY createtime) AS next_1_time,
    LEAD(createtime,2) OVER(PARTITION BY cookieid ORDER BY createtime) AS next_2_time
    FROM lxw1234;


    cookieid createtime             url    rn       next_1_time             next_2_time
    -------------------------------------------------------------------------------------------
    cookie1 2015-04-10 10:00:00     url1    1       2015-04-10 10:00:02     2015-04-10 10:03:04
    cookie1 2015-04-10 10:00:02     url2    2       2015-04-10 10:03:04     2015-04-10 10:10:00
    cookie1 2015-04-10 10:03:04     1url3   3       2015-04-10 10:10:00     2015-04-10 10:50:01
    cookie1 2015-04-10 10:10:00     url4    4       2015-04-10 10:50:01     2015-04-10 10:50:05
    cookie1 2015-04-10 10:50:01     url5    5       2015-04-10 10:50:05     2015-04-10 11:00:00
    cookie1 2015-04-10 10:50:05     url6    6       2015-04-10 11:00:00     NULL
    cookie1 2015-04-10 11:00:00     url7    7       1970-01-01 00:00:00     NULL
    cookie2 2015-04-10 10:00:00     url11   1       2015-04-10 10:00:02     2015-04-10 10:03:04
    cookie2 2015-04-10 10:00:02     url22   2       2015-04-10 10:03:04     2015-04-10 10:10:00
    cookie2 2015-04-10 10:03:04     1url33  3       2015-04-10 10:10:00     2015-04-10 10:50:01
    cookie2 2015-04-10 10:10:00     url44   4       2015-04-10 10:50:01     2015-04-10 10:50:05
    cookie2 2015-04-10 10:50:01     url55   5       2015-04-10 10:50:05     2015-04-10 11:00:00
    cookie2 2015-04-10 10:50:05     url66   6       2015-04-10 11:00:00     NULL
    cookie2 2015-04-10 11:00:00     url77   7       1970-01-01 00:00:00     NULL

    --逻辑与LAG一样，只不过LAG是往上，LEAD是往下。

FIRST_VALUE

取分组内排序后，截止到当前行，第一个值

    SELECT cookieid,
    createtime,
    url,
    ROW_NUMBER() OVER(PARTITION BY cookieid ORDER BY createtime) AS rn,
    FIRST_VALUE(url) OVER(PARTITION BY cookieid ORDER BY createtime) AS first1
    FROM lxw1234;

    cookieid  createtime            url     rn      first1
    ---------------------------------------------------------
    cookie1 2015-04-10 10:00:00     url1    1       url1
    cookie1 2015-04-10 10:00:02     url2    2       url1
    cookie1 2015-04-10 10:03:04     1url3   3       url1
    cookie1 2015-04-10 10:10:00     url4    4       url1
    cookie1 2015-04-10 10:50:01     url5    5       url1
    cookie1 2015-04-10 10:50:05     url6    6       url1
    cookie1 2015-04-10 11:00:00     url7    7       url1
    cookie2 2015-04-10 10:00:00     url11   1       url11
    cookie2 2015-04-10 10:00:02     url22   2       url11
    cookie2 2015-04-10 10:03:04     1url33  3       url11
    cookie2 2015-04-10 10:10:00     url44   4       url11
    cookie2 2015-04-10 10:50:01     url55   5       url11
    cookie2 2015-04-10 10:50:05     url66   6       url11
    cookie2 2015-04-10 11:00:00     url77   7       url11

LAST_VALUE

取分组内排序后，截止到当前行，最后一个值

    SELECT cookieid,
    createtime,
    url,
    ROW_NUMBER() OVER(PARTITION BY cookieid ORDER BY createtime) AS rn,
    LAST_VALUE(url) OVER(PARTITION BY cookieid ORDER BY createtime) AS last1
    FROM lxw1234;


    cookieid  createtime            url    rn       last1  
    -----------------------------------------------------------------
    cookie1 2015-04-10 10:00:00     url1    1       url1
    cookie1 2015-04-10 10:00:02     url2    2       url2
    cookie1 2015-04-10 10:03:04     1url3   3       1url3
    cookie1 2015-04-10 10:10:00     url4    4       url4
    cookie1 2015-04-10 10:50:01     url5    5       url5
    cookie1 2015-04-10 10:50:05     url6    6       url6
    cookie1 2015-04-10 11:00:00     url7    7       url7
    cookie2 2015-04-10 10:00:00     url11   1       url11
    cookie2 2015-04-10 10:00:02     url22   2       url22
    cookie2 2015-04-10 10:03:04     1url33  3       1url33
    cookie2 2015-04-10 10:10:00     url44   4       url44
    cookie2 2015-04-10 10:50:01     url55   5       url55
    cookie2 2015-04-10 10:50:05     url66   6       url66
    cookie2 2015-04-10 11:00:00     url77   7       url77

如果不指定ORDER BY，则默认按照记录在文件中的偏移量进行排序，会出现错误的结果

    SELECT cookieid,
    createtime,
    url,
    FIRST_VALUE(url) OVER(PARTITION BY cookieid) AS first2  
    FROM lxw1234;

    cookieid  createtime            url     first2
    ----------------------------------------------
    cookie1 2015-04-10 10:00:02     url2    url2
    cookie1 2015-04-10 10:00:00     url1    url2
    cookie1 2015-04-10 10:03:04     1url3   url2
    cookie1 2015-04-10 10:50:05     url6    url2
    cookie1 2015-04-10 11:00:00     url7    url2
    cookie1 2015-04-10 10:10:00     url4    url2
    cookie1 2015-04-10 10:50:01     url5    url2
    cookie2 2015-04-10 10:00:02     url22   url22
    cookie2 2015-04-10 10:00:00     url11   url22
    cookie2 2015-04-10 10:03:04     1url33  url22
    cookie2 2015-04-10 10:50:05     url66   url22
    cookie2 2015-04-10 11:00:00     url77   url22
    cookie2 2015-04-10 10:10:00     url44   url22
    cookie2 2015-04-10 10:50:01     url55   url22

    SELECT cookieid,
    createtime,
    url,
    LAST_VALUE(url) OVER(PARTITION BY cookieid) AS last2  
    FROM lxw1234;

    cookieid  createtime            url     last2
    ----------------------------------------------
    cookie1 2015-04-10 10:00:02     url2    url5
    cookie1 2015-04-10 10:00:00     url1    url5
    cookie1 2015-04-10 10:03:04     1url3   url5
    cookie1 2015-04-10 10:50:05     url6    url5
    cookie1 2015-04-10 11:00:00     url7    url5
    cookie1 2015-04-10 10:10:00     url4    url5
    cookie1 2015-04-10 10:50:01     url5    url5
    cookie2 2015-04-10 10:00:02     url22   url55
    cookie2 2015-04-10 10:00:00     url11   url55
    cookie2 2015-04-10 10:03:04     1url33  url55
    cookie2 2015-04-10 10:50:05     url66   url55
    cookie2 2015-04-10 11:00:00     url77   url55
    cookie2 2015-04-10 10:10:00     url44   url55
    cookie2 2015-04-10 10:50:01     url55   url55

如果想要取分组内排序后最后一个值，则需要变通一下：

    SELECT cookieid,
    createtime,
    url,
    ROW_NUMBER() OVER(PARTITION BY cookieid ORDER BY createtime) AS rn,
    LAST_VALUE(url) OVER(PARTITION BY cookieid ORDER BY createtime) AS last1,
    FIRST_VALUE(url) OVER(PARTITION BY cookieid ORDER BY createtime DESC) AS last2
    FROM lxw1234
    ORDER BY cookieid,createtime;

    cookieid  createtime            url     rn     last1    last2
    -------------------------------------------------------------
    cookie1 2015-04-10 10:00:00     url1    1       url1    url7
    cookie1 2015-04-10 10:00:02     url2    2       url2    url7
    cookie1 2015-04-10 10:03:04     1url3   3       1url3   url7
    cookie1 2015-04-10 10:10:00     url4    4       url4    url7
    cookie1 2015-04-10 10:50:01     url5    5       url5    url7
    cookie1 2015-04-10 10:50:05     url6    6       url6    url7
    cookie1 2015-04-10 11:00:00     url7    7       url7    url7
    cookie2 2015-04-10 10:00:00     url11   1       url11   url77
    cookie2 2015-04-10 10:00:02     url22   2       url22   url77
    cookie2 2015-04-10 10:03:04     1url33  3       1url33  url77
    cookie2 2015-04-10 10:10:00     url44   4       url44   url77
    cookie2 2015-04-10 10:50:01     url55   5       url55   url77
    cookie2 2015-04-10 10:50:05     url66   6       url66   url77
    cookie2 2015-04-10 11:00:00     url77   7       url77   url77