hive中同列多行数据组合的方法以及array to string要点(行转列)

1. 同列多行数据组合成一个字段cell的方法， top N 问题的hive方案 如下：

hive 列转行 to json与to array  list set等复杂结构，hive topN的提取的窗口统计方法


   
    select
                ll,
            collect_list(n) ,  -- 将topN 转换成 List or Json with the help of collect_set(xx) collect_list(xx)
            collect_list(nn),
            collect_list(ll),
            collect_list(dd)
    from
            (
                    select
                            concat(''', n, ''') as nn,
                            n                          ,
                            ll                         ,
                            concat_ws(":", concat('\'', n, '\''), ll) as dd ,

                                  row_number() over (partition by ll order by n desc ) as num1     -- 某用户的所有文章点击率排序
                    from
                            (
                                   select 1 as n, '4' as ll

                                    UNION all

                                    SELECT 2 as n, '4' as ll

                                    UNION all

                                    select 3 as n, '5' as ll

                                    UNION all

                                    SELECT 4 as n, '5' as ll
                                UNION all

                                    SELECT 5 as n, '4' as ll

                                    UNION all

                                    select 6 as n, '5' as ll

                                    UNION all

                                    SELECT 7 as n, '5' as ll

                                UNION all

                                    SELECT 8 as n, '4' as ll

                                    UNION all

                                    select 9 as n, '5' as ll

                                    UNION all

                                    SELECT 10 as n, '5' as ll
                            )
                            a

            )
            c
            where num1 <= 3      -- 筛选top 3
    group by
            ll

2. 建表存储list类型数据的方法以及注意点

CREATE TABLE if not exists celebrity_basic_info 
(
    author_id bigint COMMENT 'id',

    area array<string> COMMENT '复杂类型的数据'
   

) COMMENT '-----'
PARTITIONED BY
(
        dt string
)

ROW FORMAT DELIMITED FIELDS TERMINATED BY '	' COLLECTION ITEMS TERMINATED BY ',' STORED AS textfile ;  --这里要注意存储时的序列化转换 collection item 的分隔符。

3. 将array<string>类型数据转成string显示的方法

select  
author_id       ,
concat( case when size(area)=-1 then '[' else '["' end,concat_ws('","'  , area )            , case when size(area)=-1 then ']' else '"]' end)  --组装拼接成json list
 from  celebrity_basic_info