developer-roadmap/src/data/courses/sql-mastery/chapters/sql-basics/lessons/expressions-in-select.md

title	description	order	type
Expressions in SELECT	Learn the basics of SQL, the language for querying databases.	110	lesson-challenge

Apart from columns and constants we discussed in the previous lessons, you can also use expressions in the SELECT statement.

Expressions are any valid combination of columns, constants, and operators.

Taking the same books table from our previous lesson:

id	title	author	price
1	The Great Gatsby	F. Scott Fitzgerald	10.99
2	1984	George Orwell	12.99
3	To Kill a Mockingbird	Harper Lee	8.99

Let's say we are running a sale and want to add a 1 dollar discount to all books before displaying them. We can do this by using the following query:

SELECT title, author, price - 1 AS price
FROM books;

The output will be:

id	title	author	price
1	The Great Gatsby	F. Scott Fitzgerald	9.99
2	1984	George Orwell	11.99
3	To Kill a Mockingbird	Harper Lee	7.99

You can have any valid expression in the SELECT statement e.g. price - 1, price + 1, price * 2, price / 2, etc.

Combining Columns and Expressions

You can also use multiple columns in expressions. Let's say that instead of having the hardcoded discount of 1 dollar to all the books, we want to make it configurable based on the book.

Let's say we have added a new column discount to the books table. Our table now looks like this:

id	title	author	price	discount
1	The Great Gatsby	F. Scott Fitzgerald	10.99	1
2	1984	George Orwell	12.99	2
3	To Kill a Mockingbird	Harper Lee	8.99	3

We want to display the title, author, price, and price - discount as final_price columns.

SELECT 
    title,
    price, 
    discount,
    price - discount AS final_price,
FROM 
    books;

The output will be:

title	price	discount	final_price
The Great Gatsby	10.99	1	9.99
1984	12.99	2	10.99
To Kill a Mockingbird	8.99	3	5.99

Challenge

Given the same books table, i.e.

id	title	author	price
1	The Great Gatsby	F. Scott Fitzgerald	10.99
2	1984	George Orwell	12.99
3	To Kill a Mockingbird	Harper Lee	8.99

Write an SQL query to display the title, author, price, and price * 100 as cent_price columns. Your output should be:

title	author	price	cent_price
The Great Gatsby	F. Scott Fitzgerald	10.99	1099
1984	George Orwell	12.99	1299
To Kill a Mockingbird	Harper Lee	8.99	899