Column and Table Alias in Postgres

Whenever we want to give a temporary name to a table or a column, we can use alias and they are really helpful in many cases.

Column Alias

Syntax:

column_name AS alias_name //AS keyword is optional.

That’s it.

We don’t really need alias if we just want simple columns to be shown in the results. We only need in some cases like what if we concat two columns data? Then what will be the name for the result column?

For example, 

SELECT address || ', ' || city || ', ' || postal_code FROM customers;

//Output

?column?
"Obere Str. 57, Berlin, 12209"
"Avda. de la Constitución 2222, México D.F., 05021"
"Mataderos  2312, México D.F., 05023"
"120 Hanover Sq., London, WA1 1DP"
....
....
....

So, as we can  see in the query above, Postgres is confused to decide the column name as there are multiple columns in results concatenated.

So, to remove the confusion and to represent the data that makes sense we can just add column alias ‘Address’.

Lets look at the query results:

SELECT address || ', ' || city || ', ' || postal_code AS Address
FROM customers;

//Output

address
"Obere Str. 57, Berlin, 12209"
"Avda. de la Constitución 2222, México D.F., 05021"
"Mataderos  2312, México D.F., 05023"
....
....
....

As we can see in the query results above, now the column has a meaningful name.

Table Alias

Similar Syntax as column alias:

table_name AS alias_name //AS keyword is optional.

That’s it.

You’ve seen many times, the use of tables alias, especially in joins.

For example,

SELECT a.column, b.column FROM table a JOIN table b WHERE a.column = b.column;

Those are table alias.

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