hive中group by的时候
select col_1,col_2 from table_name group by col_1;
会提示：
FAILED: SemanticException [Error 10025]: Line 1:12 Expression not in GROUP BY key ‘col_2′
这里网上查了下，有两种解决方法：
1、不关心col_2的值，且有多个col_2，那么语句改成
select col_1, collect_set( col_2 )[0] from table_name group by col_1;
2、如果每个col_2的值不同且关心col_2的值，那么可以改成
select col_1,col_2 from table_name group by col_1,col_2;
http://one-line-it.blogspot.com/2012/11/hive-expression-not-in-group-by-key.html