在SQL中结合两列

Question

我想以这样一种方式组合两列，即在第一列下面添加第二列。 对于如：

Col 1: A B C 
Col 2: D E F 

结果：

Col : A B C D E F 

Answer 1

做一个UNION ALL拿到两列一个单柱：

select col1 from tablename 
UNION ALL 
select col2 from tablename 

如果你绝对要前COL2值COL1值，将其包装在派生表中并添加一个ORDER BY：

select col from 
(
    select col1 as col, 1 as ob from tablename 
    UNION ALL 
    select col2, 2 as ob from tablename 
) dt 
order by ob 

Answer 2

SELECT CONCAT(col1, col2) AS col FROM table