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:
SELECT column1, column2....
FROM table_name AS alias_name
WHERE [condition];
列的别名语法:
SELECT column_name AS alias_name
FROM table_name
WHERE [condition];
实例
创建 COMPANY 表（下载 COMPANY SQL 文件 ），数据内容如下：
lectcodedb# select * from COMPANY;
id | name | age | address | salary
----+-------+-----+-----------+--------
1 | Paul | 32 | California| 20000
2 | Allen | 25 | Texas | 15000
3 | Teddy | 23 | Norway | 20000
4 | Mark | 25 | Rich-Mond | 65000
5 | David | 27 | Texas | 85000
6 | Kim | 22 | South-Hall| 45000
7 | James | 24 | Houston | 10000
(7 rows)
创建 DEPARTMENT 表（下载 COMPANY SQL 文件 ），数据内容如下：
lectcodedb=# SELECT * from DEPARTMENT;
id | dept | emp_id
----+-------------+--------
1 | IT Billing | 1
2 | Engineering | 2
3 | Finance | 7
4 | Engineering | 3
5 | Finance | 4
6 | Engineering | 5
7 | Finance | 6
(7 rows)
下面我们分别用 C 和 D 表示 COMPANY 表和 DEPAERMENT 表的别名：
lectcodedb=# 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：
id | name | age | dept
----+-------+-----+------------
1 | Paul | 32 | IT Billing
2 | Allen | 25 | Engineering
7 | James | 24 | Finance
3 | Teddy | 23 | Engineering
4 | Mark | 25 | Finance
5 | David | 27 | Engineering
6 | Kim | 22 | Finance
(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：
lectcodedb=# 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：
company_id | company_name | age | dept
------------+--------------+-----+------------
1 | Paul | 32 | IT Billing
2 | Allen | 25 | Engineering
7 | James | 24 | Finance
3 | Teddy | 23 | Engineering
4 | Mark | 25 | Finance
5 | David | 27 | Engineering
6 | Kim | 22 | Finance
(7 rows)