What's returned when you run this:
SELECT DISTINCT rel_value
FROM agr.dbo.relvalue AS relvalue
WHERE (attribute_id = 'A0')
AND (rel_attr_id = 'ZL')
AND rel_value LIKE 'U%'
For fast, accurate and documented assistance in answering your questions, please read this article.
Understanding and using APPLY, (I) and (II) Paul White
Hidden RBAR: Triangular Joins / The "Numbers" or "Tally" Table: What it is and how it replaces a loop Jeff Moden