将两列合并为一个

Question

我想将两列合并为一列，其中一列有空值。它看起来像这样：

| Order Number | MOP | MOP2 | 
| 12345  | Cash |  | 
| 12346  | Credit |  | 
| 12347  | Visa | Cash | 
| 12348  | Credit |  | 

查询我运行如下所示：

Select 
    ORDER.OrderHistory.OrderNo 
    ,ORDER.OrderHistory.MOP 
    ,ORDER.OrderHistory.MOP2 
From 
    ORDER.OrderHistory 

我试图让它看起来像这样：

| Order Number | MOP | 
| 12345  | Cash | 
| 12346  | Credit | 
| 12347  | Visa | 
| 12347  | Cash | 
| 12348  | Credit | 

Answer 1

就union两个列放入数据集中的同一列：

-- This query will return all your data rows 
select o.OrderNo 
     ,o.MOP 
from ORDER.OrderHistory as o 

union all 

-- And then this one will get all where the MOP2 column is not null 
select o.OrderNo 
     ,o.MOP2 
from ORDER.OrderHistory as o 
where o.MOP2 is not null