dspace metadata field usage postgresql query

dspace-metadata-fields.md

which metadata fields are being used by dspace?

SELECT
  element,
  qualifier,
  scope_note,
  count(*)
FROM metadatavalue
JOIN metadatafieldregistry 
  ON metadatavalue.metadata_field_id = metadatafieldregistry.metadata_field_id
GROUP BY
  metadatafieldregistry.element,
  metadatafieldregistry.qualifier,
  metadatafieldregistry.scope_note
ORDER BY ELEMENT asc

if you're not concerned about the counts, you could simplify things by using a SELECT DISTINCT query and removing the GROUP BY block.