PostgreSQL 别名

我们可以用 SQL 重命名一张表或者一个字段的名称，这个名称就叫着该表或该字段的别名。

创建别名是为了让表名或列名的可读性更强。

SQL 中 使用 AS 来创建别名。

语法

表的别名语法:

1SELECT column1, column2....
2FROM table_name AS alias_name
3WHERE [condition];

列的别名语法:

1SELECT column_name AS alias_name
2FROM table_name
3WHERE [condition];

实例

创建 COMPANY 表（下载 COMPANY SQL 文件 ），数据内容如下：

1runoobdb# select * from COMPANY;
2 id | name  | age | address   | salary
3----+-------+-----+-----------+--------
4  1 | Paul  |  32 | California|  20000
5  2 | Allen |  25 | Texas     |  15000
6  3 | Teddy |  23 | Norway    |  20000
7  4 | Mark  |  25 | Rich-Mond |  65000
8  5 | David |  27 | Texas     |  85000
9  6 | Kim   |  22 | South-Hall|  45000
10  7 | James |  24 | Houston   |  10000
11(7 rows)

创建 DEPARTMENT 表（下载 COMPANY SQL 文件 ），数据内容如下：

1runoobdb=# SELECT * from DEPARTMENT;
2 id | dept        | emp_id
3----+-------------+--------
4  1 | IT Billing  |      1
5  2 | Engineering |      2
6  3 | Finance     |      7
7  4 | Engineering |      3
8  5 | Finance     |      4
9  6 | Engineering |      5
10  7 | Finance     |      6
11(7 rows)

下面我们分别用 C 和 D 表示 COMPANY 表和 DEPAERMENT 表的别名：

1runoobdb=# SELECT C.ID, C.NAME, C.AGE, D.DEPT FROM COMPANY AS C, DEPARTMENT AS D WHERE  C.ID = D.EMP_ID;

得到结果如下：

1id | name  | age |  dept
2----+-------+-----+------------
3  1 | Paul  |  32 | IT Billing
4  2 | Allen |  25 | Engineering
5  7 | James |  24 | Finance
6  3 | Teddy |  23 | Engineering
7  4 | Mark  |  25 | Finance
8  5 | David |  27 | Engineering
9  6 | Kim   |  22 | Finance
10(7 rows)

下面，我们用 COMPANY_ID 表示 ID 列，COMPANY_NAME 表示 NAME 列，来展示列别名的用法：

1runoobdb=# SELECT C.ID AS COMPANY_ID, C.NAME AS COMPANY_NAME, C.AGE, D.DEPT  FROM COMPANY AS C, DEPARTMENT AS D WHERE  C.ID = D.EMP_ID;

得到结果如下：

1company_id | company_name | age | dept
2------------+--------------+-----+------------
3      1     | Paul         |  32 | IT Billing
4      2     | Allen        |  25 | Engineering
5      7     | James        |  24 | Finance
6      3     | Teddy        |  23 | Engineering
7      4     | Mark         |  25 | Finance
8      5     | David        |  27 | Engineering
9      6     | Kim          |  22 | Finance
10(7 rows)