平時很少用到map型別，這次用到了記錄一下。

適用場景：行轉列，且mid的key個數可能不一樣的情況。
舉個栗子：

 1 select 
 2     mid,
 3     tags['電影'] as movie,
 4     tags['音樂'] as music
 5 from(
 6     select 
 7         mid,
 8         str_to_map(concat_ws(',',collect_list(concat(key,":",value)))) as tags 
 9     from (
10         select
11             mid,
 
12             key,
13             concat_ws('-',collect_list(value))as value
14         from(
15             select 1 as mid,'電影' as key,'驚悚' as value
16             union ALL
17             select 1 as mid,'音樂' as key,'搖滾' as value 
18             union ALL
19             select 1 as mid,'電影' as key
 
,'喜劇' as value 
20         ) a
21         group by 
22             mid,key
23     )t
24     group by 
25         mid
26 ) tt

構造資料：

執行結果：