What common queries appear across many dataset definitions?

[inglesp]

It has always been a goal that ehrQL's composability should allow us to provide reusable variables for researchers to use out of the box. We already provide some, including patients.age_on and practice_registrations.spanning.

We should review existing ehrQL code (via this search should find all projects using ehrQL) and look for common patterns that we could add to the ehrQL package. These could either be more methods on tables (like patients.age_on) or more complicated queries, such as BMI or ethnicity, which do not necessarily live on a table.

This ticket does not include any implementation work.