Learn SQL in a Month of Lunches

13 Using variables

We’ve written and executed a lot of SQL queries so far, and a good number of those queries involved filtering the results on specific values. Through many examples, we’ve seen how to filter on a particular order or title ID, customer name, or date range, and every time, we’ve specified the literal value for filtering in our SQL. A literal value is specific, such as the number 4 or the date 2020-10-06. Using literal values is helpful for learning and practice, but when you use SQL outside this book, you’ll need to write more flexible queries.

If you want to look at the total sales of a title for a given month, such as March 2021, you can write a query to do that now. But what if you want to run a similar query for April or need ...