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：

									yssmxdb# 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：

									yssmxdb=# 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：

									yssmxdb=# 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：

									yssmxdb=# 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)