Column Aliases in PostgreSQL

A column alias in PostgreSQL assigns a temporary display name to a column or expression in the SELECT list. The alias exists only for the duration of the query — it is not stored in the database, does not rename any table column, and has no effect on the underlying data.

Syntax

SELECT column_name AS alias_name
FROM table_name;

The AS keyword is optional. Both of the following are valid and equivalent:

SELECT unit_price AS price FROM products;
SELECT unit_price price FROM products;

You can alias any expression, not just bare column references:

SELECT expression AS alias_name
FROM table_name;

When an alias contains spaces or special characters, wrap it in double quotes:

SELECT unit_price * stock_qty AS "inventory value"
FROM products;

Practical Example

Create a sample order table and use aliases to produce readable output:

CREATE TABLE orders (
  id           SERIAL PRIMARY KEY,
  reference    VARCHAR(20) NOT NULL UNIQUE,
  customer_id  INT NOT NULL,
  subtotal     NUMERIC(10, 2) NOT NULL,
  tax_rate     NUMERIC(5, 4) NOT NULL DEFAULT 0.08,
  placed_at    TIMESTAMPTZ NOT NULL DEFAULT now()
);

INSERT INTO orders (reference, customer_id, subtotal, tax_rate) VALUES
  ('ORD-1001', 42, 129.99, 0.08),
  ('ORD-1002', 17,  49.50, 0.10),
  ('ORD-1003', 99, 310.00, 0.08),
  ('ORD-1004', 42,  22.75, 0.05);

Rename a column heading:

SELECT reference AS order_ref, placed_at AS ordered_on
FROM orders;

Result headings change from reference / placed_at to order_ref / ordered_on.

Alias a computed expression:

Without an alias, PostgreSQL labels computed columns with ?column?:

-- Unhelpful heading: ?column?
SELECT reference, subtotal * (1 + tax_rate)
FROM orders;

Add an alias for a meaningful heading:

SELECT
  reference,
  subtotal,
  tax_rate,
  subtotal * (1 + tax_rate) AS total_with_tax
FROM orders
ORDER BY total_with_tax DESC;

Use an alias in ORDER BY:

Because ORDER BY is evaluated after SELECT, you can reference the alias:

SELECT
  reference,
  EXTRACT(EPOCH FROM (now() - placed_at)) / 3600 AS hours_since_order
FROM orders
ORDER BY hours_since_order DESC;

Inspect output column names:

-- Use psql \g or \x to see column names in vertical format
SELECT reference AS order_ref, subtotal AS amount FROM orders LIMIT 1;

Where Aliases Can and Cannot Be Used

Workaround when you need a computed alias in WHERE: wrap the query in a subquery or CTE:

-- Use a subquery to filter on a computed alias
SELECT *
FROM (
  SELECT reference, subtotal * (1 + tax_rate) AS total_with_tax
  FROM orders
) t
WHERE total_with_tax > 100;

Testing with Vela

When refactoring queries to use aliases — for example, renaming output columns to match a new API contract — use Vela’s database branching to test the change against a production-like copy before rolling it out. Create a branch, run the updated queries, verify that application code consuming the renamed columns behaves correctly in your CI environment, and then promote the change to production with confidence.

Production Tips

• Always include AS explicitly even though it is optional — it signals intent and makes diffs easier to review.
• Use snake_case aliases to match PostgreSQL’s native identifier casing (total_with_tax, not TotalWithTax) — unquoted identifiers are folded to lowercase.
• Wrap aliases with spaces or special characters in double quotes; avoid them in application-facing column names to reduce quoting overhead in downstream code.
• Do not shadow existing column names with aliases unless intentional — it can cause confusion when queries are nested as subqueries.
• In ORM-generated queries or reporting tools that read column names programmatically, consistent alias naming across queries prevents field-mapping bugs.
• If an alias is defined in a SELECT and you need it in HAVING, wrap the query in a subquery or use a CTE rather than repeating the expression multiple times.