Constant HOLDER 

const HOLDER: &str = "((agent_uid <> '' AND ?2 <> '' AND agent_uid = ?2) \
                      OR ((agent_uid = '' OR ?2 = '') AND agent = ?1 COLLATE NOCASE))";

The holder test, as the work queue’s: by UID when the row and the caller both have one, else by name (case-insensitively). ?1 name, ?2 UID.