PostgreSQL ALIAS語法

可以重命名表或列暫時給予另一名被稱為別名。使用表別名是指在一個特定的PostgreSQL表重命名表。重命名是一個臨時的變化，在數據庫中實際的表的名稱不會改變。

列別名用來重命名表中的列某一PostgreSQL查詢的目的。

語法:

表別名的基本語法如下：

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

列別名的基本語法如下：

SELECT column_name AS alias_name
FROM table_name
WHERE [condition];

語法:

考慮以下兩個表：（一）COMPANY 表如下：

testdb=# 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)

（b）另一表是DEPARTMENT 如下：

 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)

以下是使用表的別名，在這裡我們使用C和D分別為COMPANY 和DEPARTMENT 表的別名：

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

以上PostgreSQL的表會產生以下結果：

 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)

讓我們看一個例子company_id是ID列的別名，COMPANY_NAME是name的別名，列別名的用法：

testdb=# 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;

以上PostgreSQL的表會產生以下結果：

 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)