You can easily create test data to help debug SQL statements:
with data (key, value) as
( values ('key1', 'a')
, ('key2', null)
, ('key3', 'z')
)
select 'min', min(coalesce(value,'')) from data
union
select 'max', max(coalesce(value,'')) from dataDisclaimer: Thoughts and opinions are my own, and do not reflect the views of any employer, family member, friend, or anyone else. Some links may be affiliate links, but I don't link to anything I don't use myself.