What is count param in spring boot actuator healthcheck?

Question

I've setup my app with actuator, and I see that it's running the following:

select count(?) from systables

What is the ? in this? I would assume it's not *.

Is there a way I can customize this query or param?

I see the following in the code:

import org.apache.tomcat.jdbc.pool.DataSource;
import org.apache.tomcat.jdbc.pool.jmx.ConnectionPool;


dataSource.setValidationQuery("select 1");