# Example_Queries

#### Clair Blacketer

#### September 29, 2020

The query below will find all standard concepts in the Visit domain that do not have any ancestors. These are considered “top-level” visit concepts and can be used to define categories of visits in cohort definitions. For example, the Inpatient Visit concept 9201 subsumes the concepts for Inpatient Hospital and Inpatient in Psychiatric Facility. Instead of creating a concept set with all of these terms to define an inpatient visit you can use 9201 and all of it’s descendants, a concept found using the top-level query.

WITH top_level AS (SELECT concept_id, concept_name FROM concept LEFT JOIN concept_ancestor ON concept_id=descendant_concept_id AND ancestor_concept_id!=descendant_concept_id WHERE domain_id=‘Visit’ AND standard_concept=‘S’ AND ancestor_concept_id IS NULL ) SELECT top_level.concept_id, top_level.concept_name, descendant.concept_id, descendant.concept_name FROM concept_ancestor JOIN top_level ON top_level.concept_id = ancestor_concept_id JOIN concept descendant ON descendant.concept_id = descendant_concept_id WHERE descendant.domain_id = ‘Visit’;