如果我希望排序只应用于一个UNION，请使用UNION ALL:

Select id,name,age
From Student
Where age < 15
Union all
Select id,name,age
From 
(
Select id,name,age
From Student
Where Name like "%a%"
Order by name
)

可以用这个:

Select id,name,age
From Student
Where age < 15
Union ALL
SELECT * FROM (Select id,name,age
From Student
Where Name like "%a%")

正如其他答案所述，在最后一个UNION之后的ORDER BY应该适用于由UNION连接的两个数据集。

我有两个使用不同表但相同列的数据集。上一个联盟之后的命令仍然没有起作用。

为ORDER BY子句中使用的列使用别名可以达到目的。

SELECT Name, Address FROM Employee 
UNION
SELECT Customer_Name, Address FROM Customer
ORDER BY customer_name;   --Won't work

解决方案是使用别名User_Name，如下所示:

SELECT Name AS User_Name, Address FROM Employee 
UNION
SELECT Customer_Name AS User_Name, Address FROM Customer
ORDER BY User_Name; 

为什么不用TOP X呢?

SELECT pass1.* FROM 
 (SELECT TOP 2000000 tblA.ID, tblA.CustomerName 
  FROM TABLE_A AS tblA ORDER BY 2) AS pass1
UNION ALL 
SELECT pass2.* FROM 
  (SELECT TOP 2000000 tblB.ID, tblB.CustomerName 
   FROM TABLE_B AS tblB ORDER BY 2) AS pass2

TOP 2000000是一个任意的数字，它大到足以捕获所有的数据。根据您的要求进行调整。

只写

Select id,name,age
From Student
Where age < 15
Union
Select id,name,age
From Student
Where Name like "%a%"
Order by name

顺序被应用到完整的结果集

顺序顺序应用在并集之后，所以 在语句的末尾添加一个order by子句:

Select id,name,age
From Student
Where age < 15
Union
Select id,name,age
From Student
Where Name like '%a%'
Order By name