Question

I have this query that I’m running in Java.

select book from com where genre=?;

I set the parameter for genre dynamically. Is there a way to sometimes set the parameter so that all data is selected?

Answer 1

The usual trick is to set a separate parameter for selecting everything:

SELECT book FROM com WHERE genre=? OR 1=?

When you set the second parameter to 0, filtering by genre is used, but when you set it to 1, everything is returned.

If you are willing to switch to using named JDBC parameters, you could rewrite with one parameter, and use null to mean “select everything”:

SELECT book FROM com WHERE genre=:genre_param OR :genre_param is null