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      PostgreSQL as

      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,数据内容如下:

      axihedb# 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,数据内容如下:

      axihedb=# 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:

      axihedb=# 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:

      axihedb=# 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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