PostgreSQL - ALIAS Syntax
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.
The column aliases are used to rename a table's columns for the purpose of a particular PostgreSQL query.
SyntaxThe basic syntax of table alias is as follows −
SELECT column1, column2.... FROM table_name AS alias_name WHERE [condition];
The basic syntax of column alias is as follows −
SELECT column_name AS alias_name FROM table_name WHERE [condition];
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) 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)
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;
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)
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;
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)
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