postgresql alias(别名)——迹忆客-ag捕鱼王app官网

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。并且创建的这个别名表只是一张临时表

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];

示例

创建 ，数据内容如下：

jiyik_db# 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 ，数据内容如下：

jiyik_db=# 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：

jiyik_db=# select c.id, c.name, c.age, d.dept from company as c, department as d where  c.id = d.emp_id;

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：

jiyik_db=# 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;

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)