Hive与MySQL的不同之GROUP BY

Hive:

DESC city_info
0 city_id string
1 parent_id string
2 name string
3 type string

SELECT * FROM city_info a GROUP BY city_id;
(tok_table_or_col city_id)
0 100000
1 110000
2 110100

SELECT city_id,parent_id FROM city_info a GROUP BY city_id;
会报错。

MySQL:

SELECT * FROM tb_user a GROUP BY user_name;
会出来所有列

SELECT user_name FROM tb_user a GROUP BY user_name;
会出来1列：user_name

SELECT id FROM tb_user a GROUP BY user_name;
会出来1列：id

SELECT email FROM tb_user a GROUP BY user_name;
会出来1列：email

SELECT id,email FROM tb_user a GROUP BY user_name;
会出来2列：id和email

SELECT id,user_name FROM tb_user a GROUP BY user_name;
会出来2列：id和user_name