SQLAlias(别名)

您可以通过Alias 在表或列上起一个别名，表别名的使用是在特定的SQL语句中重命名表，列别名用于重命名表的列，以用于特定的SQL查询。

Alias- 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];

Alias- 示例

请考虑以下两个表。

表1-客户表(CUSTOMERS)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 | Learnfk    |  24 | Indore    | 10000.00 |
+----+----------+-----+-----------+----------+

+-----+---------------------+-------------+--------+
|OID  | DATE                | CUSTOMER_ID | AMOUNT |
+-----+---------------------+-------------+--------+
| 102 | 2019-10-08 00:00:00 |           3 |   3000 |
| 100 | 2019-10-08 00:00:00 |           3 |   1500 |
| 101 | 2019-11-20 00:00:00 |           2 |   1560 |
| 103 | 2018-05-20 00:00:00 |           4 |   2060 |
+-----+---------------------+-------------+--------+

现在，以下代码块显示了表别名的用法。

SQL> SELECT C.ID, C.NAME, C.AGE, O.AMOUNT 
   FROM CUSTOMERS AS C, ORDERS AS O
   WHERE  C.ID=O.CUSTOMER_ID;

这将产生以下输出。

+----+----------+-----+--------+
| ID | NAME     | AGE | AMOUNT |
+----+----------+-----+--------+
|  3 | kaushik  |  23 |   3000 |
|  3 | kaushik  |  23 |   1500 |
|  2 | Khilan   |  25 |   1560 |
|  4 | Chaitali |  25 |   2060 |
+----+----------+-----+--------+

SQL> SELECT  ID AS CUSTOMER_ID, NAME AS CUSTOMER_NAME
   FROM CUSTOMERS
   WHERE SALARY IS NOT NULL;

这将产生以下输出。

+-------------+---------------+
| CUSTOMER_ID | CUSTOMER_NAME |
+-------------+---------------+
|           1 | Ramesh        |
|           2 | Khilan        |
|           3 | kaushik       |
|           4 | Chaitali      |
|           5 | Hardik        |
|           6 | Komal         |
|           7 | Learnfk         |
+-------------+---------------+