Column & Table Aliases (AS)

Reviewed & published by Brayan K

Raw column names like total_spent are fine for the database but awkward in a report, and a calculated column has no name at all until you give it one. AS lets you rename columns and tables on the fly — purely for the result of one query.

Part of the free SQL course at LearnCodingFast — hands-on lessons with examples you run in your browser, plus practice exercises and a quick quiz.

You'll learn column aliases for readable headings, table aliases that make joins compact, and the one rule that trips everyone up: where you can and can't use an alias.

What You'll Learn

• Rename columns in output with AS
• Name calculated columns
• Quote aliases that contain spaces
• Give tables short nicknames
• Why joins need table aliases
• Use aliases in ORDER BY (not WHERE)

Our Sample Table: customers

Plus a related orders table for the join example. Note the database-style column names — exactly the kind we'll dress up with aliases.

1. Column Aliases — Friendly Headings

A column alias renames a column in the result set. The table keeps its real column names; only this query's output changes. Use AS (or just a space) followed by the new name.

An alias is like a name tag at a conference. Your legal name (the column name) doesn't change — but for today, your tag says "Sam from Marketing" so everyone can read it easily.

-- The two tables this lesson uses. Run this block first;
-- every later block queries them.
CREATE TABLE customers (
    id          INTEGER PRIMARY KEY,
    full_name   TEXT,
    total_spent NUMERIC(10,2)
);
INSERT INTO customers VALUES
    (1, 'Amélie Dubois', 1240.55),
    (2, 'Lucas Martin',   980.25),
    (3, 'Mia Chen',      2310.75);

CREATE TABLE orders (
    id          INTEGER PRIMARY KEY,
    customer_id INTEGER,
    amount      NUMERIC(10,2)
);
INSERT INTO orders VALUES
    (100, 1, 420.50),
    (101, 3, 899.99),
    (102, 1, 820.00);

-- AS renames a column in the OUTPUT only
SELECT
    full_name   AS customer,
    total_spent AS "Lifetime Value"
FROM customers;

-- ✅ Expected result:
-- customer | Lifetime Value
-- Amélie Dubois | 1240.55
-- Lucas Martin | 980.25
-- Mia Chen | 2310.75

2. Naming Calculated Columns

This is where aliases stop being a nicety and become essential. A computed column like total_spent * 0.05 has no natural name — without an alias, its heading is the raw expression, and you can't reference it cleanly anywhere else.

-- Uses the customers and orders tables from the first example.
-- Calculated columns have NO name until you give them one
SELECT
    full_name,
    total_spent,
    ROUND(total_spent * 0.05, 2) AS reward_points
FROM customers;

-- ✅ Expected result:
-- full_name | total_spent | reward_points
-- Amélie Dubois | 1240.55 | 62.03
-- Lucas Martin | 980.25 | 49.01
-- Mia Chen | 2310.75 | 115.54

Your Turn: name the columns

Add the alias keyword in both blanks to produce the headings "Customer" and "Spent (USD)".

-- Uses the customers and orders tables from the first example.
-- 🎯 YOUR TURN — add two aliases, then "Try it Yourself"
-- Goal: show the name as "Customer" and the spend as "Spent (USD)".

SELECT
    full_name   ___ "Customer",      -- 👉 replace ___ with AS
    total_spent ___ "Spent (USD)"    -- 👉 replace ___ with AS
FROM customers;

-- ✅ Expected result:
-- Customer | Spent (USD)
-- Amélie Dubois | 1240.55
-- Lucas Martin | 980.25
-- Mia Chen | 2310.75

3. Table Aliases — Short Nicknames

A table alias is a short nickname you use to refer to a table throughout the query. They keep queries compact and are practically mandatory in joins, where two tables may share column names like id.

-- Uses the customers and orders tables from the first example.
-- A table alias is a short nickname for a table
SELECT o.id, o.amount, c.full_name
FROM orders   AS o
JOIN customers AS c ON c.id = o.customer_id;

-- Without aliases this would read:
--   orders.id, orders.amount, customers.full_name
--   FROM orders JOIN customers ON customers.id = orders.customer_id
-- The aliases o and c make it far shorter and clearer.

-- ✅ Expected result:
-- id | amount | full_name
-- 100 | 420.5 | Amélie Dubois
-- 101 | 899.99 | Mia Chen
-- 102 | 820 | Amélie Dubois

4. Where Aliases Work (and Don't)

This catches almost every beginner. Because of the order SQL evaluates a query, a column alias is created after WHERE runs — so you can use it in ORDER BY but not in WHERE.

-- Uses the customers and orders tables from the first example.
-- You CAN use a column alias in ORDER BY...
SELECT full_name, ROUND(total_spent * 0.05, 2) AS reward_points
FROM customers
ORDER BY reward_points DESC;   -- ✅ works in most databases

-- ...but NOT in WHERE — this errors:
--   WHERE reward_points > 50   ❌ alias unknown here
-- Use the full expression instead:
--   WHERE total_spent * 0.05 > 50   ✅

-- ✅ Expected result:
-- full_name | reward_points
-- Mia Chen | 115.54
-- Amélie Dubois | 62.03
-- Lucas Martin | 49.01

🧩 Reorder Challenge

Unscramble these lines into a query that lists each customer's name and a "tax" column (20% of spend), sorted by tax, highest first.

-- SCRAMBLED — arrange into a query that shows each
-- customer's name and a "Tax" column (total_spent * 0.2),
-- sorted by that tax, highest first.

ORDER BY tax DESC
SELECT full_name AS name,
FROM customers
total_spent * 0.2 AS tax

Why: the two SELECT expressions come first (they define name and tax), then FROM, then ORDER BY. The alias tax is usable in ORDER BY because sorting happens after SELECT assigns the alias — which is exactly why you couldn't use tax in a WHERE clause here.

🧠 Quick Recall

Predict the outcome, then reveal.

revenue — the alias replaces the column name in the result. The stored column is still total_spent.

No — WHERE runs before the alias exists. You'd get an "unknown column revenue" error. Use the full expression WHERE total_spent > 1000.

Yes — AS is optional. The column heading becomes customer. Many style guides keep AS for clarity, but it's not required.

Common Errors (and the fix)

• Alias in WHERE: WHERE reward_points > 50 fails — repeat the expression: WHERE total_spent * 0.05 > 50.
• Spaces without quotes: AS Total Price errors. Wrap multi-word aliases in double quotes: AS "Total Price".
• Mixing alias and real name in a join: once you write FROM orders o, you must use o.amount, not orders.amount — the original name is hidden.
• Single quotes for an alias: AS 'name' may be read as a string literal in strict modes. Use double quotes (or no quotes) for identifiers.

Mini-Challenge: VIP Report

Build a report with a "Name" column, a calculated "Tier Bonus" column, and a table alias. Expected headings are in the comments.

-- 🎯 MINI-CHALLENGE — uses only this lesson's ideas
-- Build a "VIP report":
--   1. Column "Name"  = full_name
--   2. Column "Tier Bonus" = total_spent * 0.10  (a calculated column)
--   3. Use a table alias 'c' for customers
--
-- ✅ Expected headings: Name | Tier Bonus

-- your query here

🎉 Lesson Complete

• ✅ Column aliases rename columns in the output only
• ✅ Calculated columns need an alias to be readable and referenceable
• ✅ Quote aliases that contain spaces: AS "Total Price"
• ✅ Table aliases keep joins short and remove ambiguity
• ✅ Aliases work in ORDER BY but not in WHERE
• ✅ Next: match text patterns with LIKE and wildcards

Practice quiz

Continue this course

• Previous: LIMIT, OFFSET, TOP & FETCH
• Next: LIKE & Wildcards — Match text patterns with LIKE, % and _
• Quick reference: SQL cheat sheet

Frequently asked questions

Is the AS keyword required for aliases?

No. AS is optional for both column and table aliases — SELECT price total and SELECT price AS total are identical. Most teams keep AS for column aliases (it reads clearly) and drop it for table aliases (SELECT * FROM orders o).

Can I use a column alias in the WHERE clause?

Usually not. WHERE is evaluated before SELECT assigns aliases, so the alias doesn't exist yet. You can reference column aliases in ORDER BY (and in GROUP BY/HAVING in some databases), but in WHERE you must repeat the full expression.

When do I need double quotes around an alias?

Only when the alias contains spaces, special characters, or you want to preserve exact casing — e.g. AS "Total Price". A simple one-word alias like total_price needs no quotes.

Why are table aliases almost mandatory in joins?

When two tables both have an 'id' column, the database can't tell which you mean. A short table alias (o.id vs c.id) disambiguates every column and makes long join queries far shorter and easier to read.

Do aliases change the actual table?

Never. An alias only renames a column or table for the duration of one query's result. The stored schema — real column and table names — is completely untouched.

Related lessons

• SELECT Statement