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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:

shulanxtdb# 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:

shulanxtdb=# 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:

shulanxtdb=# 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:

shulanxtdb=# 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)

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