Postgresql 简明教程

PostgreSQL - ALIAS Syntax

您可以通过提供另一个名称暂时重命名表或列，该名称被称为 ALIAS 。使用表别名意在在特定 PostgreSQL 语句中重命名一个表。重命名是一种临时更改，实际的表名在数据库中不会更改。

You can rename a table or a column temporarily by giving another name, which is known as ALIAS. The use of table aliases means to rename a table in a particular PostgreSQL statement. Renaming is a temporary change and the actual table name does not change in the database.

列别名用于重命名表的列以便用于特定 PostgreSQL 查询。

The column aliases are used to rename a table’s columns for the purpose of a particular PostgreSQL query.

Syntax

table 别名的基本语法如下：

The basic syntax of table alias is as follows −

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

column 别名的基本语法如下：

The basic syntax of column alias is as follows −

SELECT column_name AS alias_name
FROM table_name
WHERE [condition];

Example

请查看以下两个表，（a） COMPANY 表如下所示：

Consider the following two tables, (a) COMPANY table is as follows −

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）另一张表 DEPARTMENT 如下所示：

(b) Another table is DEPARTMENT as follows −

 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)

现在，以下是 TABLE ALIAS 的用法，其中我们使用 C 和 D 作为 COMPANY 和 DEPARTMENT 表的别名，分别：

Now, following is the usage of TABLE ALIAS where we use C and D as aliases for COMPANY and DEPARTMENT tables, respectively −

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

以上给出的 PostgreSQL 语句将产生以下结果 -

The above given PostgreSQL statement will produce the following result −

 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)

让我们看一看 COLUMN ALIAS 用法的示例，其中 COMPANY_ID 是 ID 列的别名而 COMPANY_NAME 是 name 列的别名：

Let us see an example for the usage of COLUMN ALIAS where COMPANY_ID is an alias of ID column and COMPANY_NAME is an alias of name column −

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;

以上给出的 PostgreSQL 语句将产生以下结果 -

The above given PostgreSQL statement will produce the following result −

 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)