Sams Teach Yourself SQL in 24 Hours (5th Edition) (Sams Teach Yourself -- Hours)

Why won't the SELECT clause work without the FROM clause?

The SELECT clause merely tells the database what data you want to see. The FROM clause tells the database where to get the data.

When I use the ORDER BY clause and choose the option descending, what does that really do to the data?

Say that you use the ORDER BY clause and have selected the last_name from the EMPLOYEE_TBL. If you used the descending option, the order would start with the letter Z and finish with the letter A. Now, let's say that you have used the ORDER BY clause and have selected the salary from the EMPLOYEE_PAY_TBL. If you used the descending option, the order would start with the largest salary down to the lowest salary.

What advantage is there to renaming columns ?

The new column name could fit the description of the returned data more closely for a particular report.