通过使用 SQL，可以为表名称或列名称指定别名（Alias）。
SELECT column_name AS alias_name
FROM table_name;
WHERE condition;
SELECT column_name(s)
FROM table_name AS alias_name;
WHERE condition;
在本教程中，我们将使用著名的Northwind示例数据库。
以下是"Customers" 表中的数据：
| CustomerID | CustomerName | ContactName | Address | City | PostalCode | Country |
|---|---|---|---|---|---|---|
| 2 | Ana Trujillo Emparedados y helados | Ana Trujillo | Avda. de la Constitución 2222 | México D.F. | 05021 | Mexico |
| 3 | Antonio Moreno Taquería | Antonio Moreno | Mataderos 2312 | México D.F. | 05023 | Mexico |
| 4 | Around the Horn | Thomas Hardy | 120 Hanover Sq. | London | WA1 1DP | UK |
下面是选自 "Orders" 表的数据：
| OrderID | CustomerID | EmployeeID | OrderDate | ShipperID |
|---|---|---|---|---|
| 10354 | 58 | 8 | 1996-11-14 | 3 |
| 10355 | 4 | 6 | 1996-11-15 | 1 |
| 10356 | 86 | 6 | 1996-11-18 | 2 |
以下SQL语句创建两个别名，一个用于CustomerID列，另一个用于CustomerName列：
SELECT CustomerID as ID, CustomerName AS Customer
FROM Customers;
以下SQL语句创建两个别名，一个用于CustomerName列，一个用于ContactName列。注：如果别名包含空格，则需要双引号或方括号：
SELECT CustomerName AS Customer, ContactName AS [Contact Person]
FROM Customers;
以下SQL语句创建一个名为“Address”的别名，它包含四列（Address，PostalCode，City and Country）：
SELECT CustomerName, Address + ', ' + PostalCode + ', ' + City + ', ' + Country AS Address
FROM Customers;
注意：要使上面的SQL语句在MySQL中工作，请使用以下命令：
SELECT CustomerName, CONCAT(Address,', ',PostalCode,', ',City,', ',Country) AS Address
FROM Customers;
以下SQL语句选择CustomerID = 4（“围绕角”）的所有订单。我们使用“Customers”和“Orders”表，给它们分别为“c”和“o”的表别名（这里我们使用别名来使SQL更短）：
SELECT o.OrderID, o.OrderDate, c.CustomerName
FROM Customers AS c, Orders AS o
WHERE c.CustomerName="Around the Horn" AND c.CustomerID=o.CustomerID;
以下SQL语句与上述相同，但没有别名：
SELECT Orders.OrderID, Orders.OrderDate, Customers.CustomerName
FROM Customers, Orders
WHERE Customers.CustomerName="Around the Horn" AND Customers.CustomerID=Orders.CustomerID;
在下列情况下使用别名是有用的：
查询涉及多个表
用于查询函数
需要把两个或更多的列放在一起
列名长或可读性差
考虑下面两个数据表：
（a）CUSTOMERS 表，如下：
+----+----------+-----+-----------+----------+
| ID | NAME | AGE | ADDRESS | SALARY |
+----+----------+-----+-----------+----------+
| 1 | Ramesh | 32 | Ahmedabad | 2000.00 |
| 2 | Khilan | 25 | Delhi | 1500.00 |
| 3 | kaushik | 23 | Kota | 2000.00 |
| 4 | Chaitali | 25 | Mumbai | 6500.00 |
| 5 | Hardik | 27 | Bhopal | 8500.00 |
| 6 | Komal | 22 | MP | 4500.00 |
| 7 | Muffy | 24 | Indore | 10000.00 |
+----+----------+-----+-----------+----------+
（b）另一个是 ORDERS 表，如下所示：
+-----+---------------------+-------------+--------+
|OID | DATE | CUSTOMER_ID | AMOUNT |
+-----+---------------------+-------------+--------+
| 102 | 2009-10-08 00:00:00 | 3 | 3000 |
| 100 | 2009-10-08 00:00:00 | 3 | 1500 |
| 101 | 2009-11-20 00:00:00 | 2 | 1560 |
| 103 | 2008-05-20 00:00:00 | 4 | 2060 |
+-----+---------------------+-------------+--------+
下面是表别名的用法：
SQL> SELECT C.ID, C.NAME, C.AGE, O.AMOUNT
FROM CUSTOMERS AS C, ORDERS AS O
WHERE C.ID = O.CUSTOMER_ID;
上面语句的运行结果如下所示：
+----+----------+-----+--------+
| ID | NAME | AGE | AMOUNT |
+----+----------+-----+--------+
| 3 | kaushik | 23 | 3000 |
| 3 | kaushik | 23 | 1500 |
| 2 | Khilan | 25 | 1560 |
| 4 | Chaitali | 25 | 2060 |
+----+----------+-----+--------+
下面是列别名的用法：
SQL> SELECT ID AS CUSTOMER_ID, NAME AS CUSTOMER_NAME
FROM CUSTOMERS
WHERE SALARY IS NOT NULL;
其运行结果如下所示：
+-------------+---------------+
| CUSTOMER_ID | CUSTOMER_NAME |
+-------------+---------------+
| 1 | Ramesh |
| 2 | Khilan |
| 3 | kaushik |
| 4 | Chaitali |
| 5 | Hardik |
| 6 | Komal |
| 7 | Muffy |
+-------------+---------------+