PostgreSQL Aliases

What Is an Alias?

An alias is a temporary label you assign to a column or a table using the AS keyword. The alias exists only for the lifetime of the query and does not change the underlying schema. Aliases are especially useful when a column name is long, when you compute a new value with an expression, or when you need to distinguish between two copies of the same table in a self-join.

Column Aliases

A column alias renames the output header of a SELECT list item. This is purely cosmetic for the result set: it changes what the client sees in the returned columns, not the table itself.

SELECT first_name AS "First Name",
       last_name  AS "Last Name"
FROM employees;

Table Aliases

A table alias gives a shorter or more descriptive name to a table reference, which is invaluable once a query touches more than one table. Instead of repeating a long table name in every column reference, you prefix columns with the short alias.

SELECT e.first_name, e.salary
FROM employees AS e
WHERE e.salary > 50000;

Aliases with Expressions

Aliases are almost mandatory when a column is the result of a calculation, a function call, or a concatenation, since PostgreSQL would otherwise label it with an unhelpful auto-generated name like ?column?.

SELECT first_name || ' ' || last_name AS full_name,
       salary * 12 AS annual_salary
FROM employees;

• Column aliases rename output headers only, not stored column names.
• Table aliases shorten references and are required for self-joins.
• Quoted aliases ("Full Name") preserve spaces and mixed case.
• Aliases cannot be used in the WHERE clause of the same SELECT (only in ORDER BY or GROUP BY, and only sometimes).