hive 列转行—collect_set()/collect_list()/concat_ws()函数的使用场景_collect set函数用法

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一、collect_set()/collect_list():

在 Hive 中想实现按某字段分组，对另外字段进行合并，可通过collect_list()或者collect_set()实现。

• collect_set()函数与collect_list()函数：列转行专用函数，都是将分组中的某列转为一个数组返回。有时为了字段拼接效果，多和concat_ws()函数连用。

• collect_set()与collect_list()的区别：

collect_list()函数 - - 不去重
collect_set()函数 - - 去重

二、实际运用

1、创建测试表及插入数据 :

drop table test_1;
create table test_1(
id string,
cur_day string,
rule string
) 
row format delimited fields terminated by ',';

insert into test_1 values
('a','20230809','501'),('a','20230811','502'),('a','20230812','503'),('a','20230812','501'),('a','20230813','512'),('b','20230809','511'),('b','20230811','512'),('b','20230812','513'),('b','20230812','511'),('b','20230813','512'),('b','20230809','511'),('c','20230811','512'),('c','20230812','513'),('c','20230812','511'),('c','20230813','512');
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把同一分组的不同行的数据聚合成一个行

举例1：按照id，cur_day分组，取出每个id对应的所有rule（不去重）。

select id,cur_day,collect_list(rule) as rule_total  from test_1 group by id,cur_day order by id,cur_day;
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举例2：按照id，cur_day分组，取出每个id对应的所有rule（去重）。

select id,cur_day,collect_set(rule) as rule_total from test_1 group by id,cur_day order by id,cur_day;
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• 用下标可以随机取某一个

select id,cur_day,collect_list(rule)[0] as rule_one from test_1 group by id,cur_day order by id,cur_day;

select id,cur_day,collect_set(rule)[0] as rule_one from test_1 group by id,cur_day order by id,cur_day;
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• 聚合后的中的值用‘|’分隔开

select id,cur_day,concat_ws('|',collect_list(rule)) as rule_total from test_1 group by id,cur_day order by id,cur_day;

select id,cur_day,concat_ws('|',collect_set(rule)) as rule_total from test_1 group by id,cur_day order by id,cur_day;
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例子

• spark-sql : COLLECT_LIST里边字段起别名.(as等其他方式都用过,都报错.
  最后用子查询来解决)

SELECT fenceCode,
       COLLECT_LIST(STRUCT(vehicleNo, plateColor, enterTime, levaeTime, trans)) AS actInfos
FROM (
    SELECT fence_code AS fenceCode,
           veh_no AS vehicleNo,
           veh_color AS plateColor,
           enter_time AS enterTime,
           out_time AS levaeTime,
           trans
    FROM mid.ct_fence_into_out_dt where dt = 20230911  
) subquery
GROUP BY fenceCode;
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总结

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