可以通过给定另一名称被叫作别名临时重命名表或列。
使用表别名指在一个特定的SQL语句重命名表。 重命名是一个临时的变化，实际的表名称并不更改数据库中。
列别名用来命名表中的列的特定SQL查询的目的。
语法
表别名的基本语法如下：
SELECT column1, column2.... FROM table_name AS alias_name WHERE [condition];
列别名的基本语法如下：
SELECT column_name AS alias_name FROM table_name WHERE [condition];
例子：
考虑下面的两个表中，(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ORDERS表如下：
+-----+---------------------+-------------+--------+ |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 | +-----+---------------------+-------------+--------+
现在，下面是表的别名的用法：
SQL> SELECT C.ID, C.NAME, C.AGE, O.AMOUNT
FROM CUSTOMERS AS C, ORDERS AS O
WHERE C.ID = O.CUSTOMER_ID;
这将产生以下结果：
+----+----------+-----+--------+ | ID | NAME | AGE | AMOUNT | +----+----------+-----+--------+ | 3 | kaushik | 23 | 3000 | | 3 | kaushik | 23 | 1500 | | 2 | Khilan | 25 | 1560 | | 4 | Chaitali | 25 | 2060 | +----+----------+-----+--------+
以下是列别名的用法：
SQL> SELECT ID AS CUSTOMER_ID, NAME AS CUSTOMER_NAME
FROM CUSTOMERS
WHERE SALARY IS NOT NULL;
这将产生以下结果：
+-------------+---------------+ | CUSTOMER_ID | CUSTOMER_NAME | +-------------+---------------+ | 1 | Ramesh | | 2 | Khilan | | 3 | kaushik | | 4 | Chaitali | | 5 | Hardik | | 6 | Komal | | 7 | Muffy | +-------------+---------------+
