lesson 02 SQL foundations · beginner
Aliases & calculated columns
Name your results and calculate values from existing columns.
the idea
AS gives an output column a readable name. You can calculate values for each row with arithmetic. The original table stays unchanged.
tables in this lesson
The challenges use this data. Each column shows its type underneath; → marks a link to another table.
products4 columns · 6 rows
| idinteger · key | nametext | categorytext | pricereal |
|---|---|---|---|
| 1 | Notebook | Stationery | 12 |
| 2 | Desk lamp | Home | 45 |
| 3 | Keyboard | Tech | 80 |
| 4 | Pen set | Stationery | 8 |
| 5 | Headphones | Tech | 120 |
showing 5 of 6 rows
orders6 columns · 12 rows
| idinteger · key | customer_idinteger | product_idinteger | quantityinteger | statustext | ordered_attext |
|---|---|---|---|---|---|
| 101 | 1 | 1 | 2 | paid | 2025-01-01 |
| 102 | 2 | 3 | 1 | paid | 2025-01-02 |
| 103 | 1 | 2 | 1 | paid | 2025-01-05 |
| 104 | 3 | 5 | 2 | pending | 2025-01-08 |
| 105 | 4 | 4 | 5 | paid | 2025-02-01 |
showing 5 of 12 rows
example
The idea in one query. Press Run to see what it returns; running examples never affects your progress.
SELECT name, price * 2 AS double_price FROM products;
Watch for: AS names the result. It does not update the stored column. A quoted number is text, so use a numeric expression for arithmetic.
build it step by step
Each step changes one thing. Run them in order and watch the result change.
Name a calculated column. Read the stored price first. The next step multiplies it and names the result without changing the table.
step-1.sqlSELECT name, price FROM products;
Run the reference. AS gives an output column a readable name. You can calculate values for each row with arithmetic. The original table stays unchanged.
step-2.sqlSELECT name, price * 2 AS double_price FROM products;