lesson 02 SQL foundations · beginner

Aliases & calculated columns

Name your results and calculate values from existing columns.

the idea

A SELECT item can be a calculation as well as a column. AS gives the result column a name. Arithmetic on a NULL value produces NULL, so a product with no list price has no calculated price either.

Dataset: Retail

The tables the challenges use, with their first 6 rows. Under each column name: the kind of value it holds, and which table it links to.

worked example

Run these steps in order to see the idea before you write your own query. The step marked “the pattern” is what the challenges ask for. Running the example does not count toward progress.

1. 1

   See products that have a price. list_price is the unit selling price. Some products have no price recorded (NULL); this step skips those so you see real numbers first.

   step-1.sql Run

   sql›

   SELECT stock_code, description, list_price
   FROM products
   WHERE list_price IS NOT NULL
   LIMIT 10;

2. 2

   Calculate and name a column. Multiply the price, then use AS to name the new column. The challenges ask for every product—including missing prices, where the result stays NULL. That is normal, not a bug.the pattern

   example.sql Run

   sql›

   SELECT stock_code, list_price, list_price * 10 AS price_for_ten
   FROM products
   WHERE list_price IS NOT NULL
   LIMIT 12;

common mistake

Without AS, the result column is named after the expression text, which does not match the requested name.