1. concat
    說明 : 將多個字串 按照預設分隔符(空) ,拼接成一個字串
    示例 : select concat('gao','cun');
    結果 : gaocun

2. concat_ws
    說明 : 將多個字串 或者array, 按照指定分隔符(第一個引數), 拼接成一個字串
    示例 : select concat_ws('-','gao','cun',split('da,wang',','));
    結果 : gao-cun-da-wang

3. collect_set (聚合函式 UDAF)
    說明 : 將分組內 指定欄位封裝成一個set(對元素去重) 返回
 

    示例 :

4. collect_list (聚合函式 UDAF)
    說明 : 將分組內 指定欄位封裝成一個list(對元素不去重) 返回
    示例 :

5. group_concat (mysql 中函式)
    說明 : group_concat( [distinct] 要連線的欄位 [order by 排序欄位 asc/desc ] [separator ‘分隔符’] )
    示例 : select name
         , group_concat(distinct friend order by friend desc separator '@') as friends1
 

         , group_concat(friend) as friends2
    from (
             select '劉備' as name, '張飛' as friend
             union all
             select '劉備' as name, '張飛' as friend
             union all
             select '劉備' as name, '關羽' as friend
             union all
             select '劉備' as name, '趙雲' as friend
 

             union all
             select '曹操' as name, '許褚' as friend
             union all
             select '曹操' as name, '荀彧' as friend
         ) as t1
    group by name;
-- 結果
name    friends1        friends2
劉備     趙雲@張飛@關羽   張飛,張飛,關羽,趙雲
曹操     許褚@荀彧      許褚,荀彧

6. 行轉列
-- 人員表
name   friend
劉備    張飛
劉備    張飛
劉備    關羽
劉備    趙雲
曹操    許褚
曹操    荀彧
-- 統計結果
name    friends
劉備     張飛、關羽、趙雲
曹操     許褚、荀彧
-- 執行sql
with t1 as (
select '劉備' as name,'張飛' as friend union all
select '劉備' as name,'張飛' as friend union all
select '劉備' as name,'關羽' as friend union all
select '劉備' as name,'趙雲' as friend union all
select '曹操' as name,'許褚' as friend union all
select '曹操' as name,'荀彧' as friend )
select
name
,concat_ws(',', collect_set(friend)) as friends1 -- 對元素去重
,concat_ws(',', collect_list(friend)) as friends2 -- 對元素不去重

from t1
group by name;
-- 結果
name    friends1        friends2
劉備    張飛,關羽,趙雲     張飛,張飛,關羽,趙雲
曹操    許褚,荀彧         許褚,荀彧