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PostgreSQL alias


We can use SQL to rename a table or the name of a field, which is called the table or an alias for the field.

Create aliases to make table names or column names more readable.

SQL Use AS to create an alias.

Syntax

Algorithm syntax for tables:

SELECT column1, column2< /span>....
FROM table_name AS alias_name
WHERE [condition];

Algorithm syntax for columns:

SELECT column_name AS alias_name
FROM table_name
WHERE [condition];

Instance

Create a COMPANY table (COMPANY SQL file) with the following data:

runoobdb# 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
(7rows)

Create a DEPARTMENT table (download the COMPANY SQL file ) with the following data:

runoobdb=# SELECT < /span>* 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
(7rows)

Here we use C and D to represent aliases for the COMPANY table and the DEPAERMENT table:

runoobdb=# SELECT C .ID, C.NAME, C.AGE, D.DEPT FROM COMPANY AS C,< /span> DEPARTMENT AS D WHERE C.ID = D.EMP_ID;

Get the results as follows:

 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)

Here, we use COMPANY_ID for the ID column and COMPANY_NAME for the NAME column to show the usage of the column alias:

runoobdb=# 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;

Get the result as follows:

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)