Column Aliases and Expression Naming in SQL
A column alias assigns a name to an expression in the SELECT list. That name appears as the column header in the result set and can be referenced by name in specific parts of the same query.
Before this SELECT and Column Expressions
Builds toward Self-Joins
AS is what you use to name the columns in your result.
Without it, SQL names computed columns for you, and the names it chooses often look broken. Run two numbers through arithmetic and the column might come out labeled ?column? or something equally cryptic. When you share that with a manager, it looks unfinished. AS is how you put the right label on the column before it reaches anyone else.
You write the expression, write AS, then give the column whatever name makes sense. That name appears as the header in your result:
SELECT 2400 AS annual_salary, 2400 / 12 AS monthly_salaryOne row, two clearly labeled columns. The names appear exactly as you wrote them — or close to exactly, which brings up the most common alias mistake.
SQL converts unquoted alias names to lowercase. AS MonthlyRevenue produces a column called monthlyrevenue. To preserve capitals, spaces, or any formatting that makes the label readable, wrap the name in double quotes:
SELECT 8500 - 1200 AS "Net Revenue"Double quotes tell SQL to take the name literally: capitals, spaces, everything. This is also how you use SQL reserved words as column names:
Without the quotes, SQL reads from as the start of a FROM clause and errors immediately. Double-quoting the alias sidesteps the conflict.
The AS keyword itself is optional. SELECT 9 * 8 hours_worked is valid — hours_worked is the alias even without AS. Omitting it saves a word, but including it makes the intent clear at a glance. Using AS consistently is the safer habit.
You write SELECT 3000 AS MonthlyRevenue. What is the column name in the result?
9 Column Aliases and Expression Naming practice problems
Write a query to return the combined total in a single column named `total_budget`.
Write a query to return the annual salary and the monthly equivalent in a single row, with the columns named `annual_salary` and `monthly_salary`.
Write a query to return the total hours in a single column named `hours_worked`. The `AS` keyword is optional — `9 * 8 hours_worked` works the same as `9 * 8 AS hours_worked`.
Write a query to return all three figures in one row.
Write a query that returns net revenue in a column with that exact name.
Write a query that returns those two values in a single row with the required column names.
Write a query to return all three in a single row.
Write a query that returns net profit in a column with that exact name.
Write a query to return both prices in a single row.
These problems are part of the Column Aliases and Expression Naming lesson in SQLMaxx, with instant grading and a worked solution on each.
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