SELECT: choosing columns

Instead of *, list the columns you want separated by commas. It is clearer and faster, especially on big tables.

SELECT first_name, last_name, job_title
FROM employees;

You can rename a column with AS, and calculate directly:

SELECT first_name AS name,
       salary,
       salary * 12 AS yearly_salary
FROM employees;

And DISTINCT removes duplicates from the result:

SELECT DISTINCT category FROM products;