SOLUÇÃO ATUALIZADA:
SELECT UserId, First name, Last name, IsRequired, IsDeleted FROM table WHERE UserId IN (SELECT UserId FROM users GROUP BY UserId HAVING count(distinct(IsRequired)) > 1) and IsRequired = 'true'
UNION
SELECT UserId, First name, Last name, IsRequired, IsDeleted FROM table WHERE UserId IN (SELECT UserId FROM users GROUP BY UserId HAVING count(IsRequired) = 1)
Consulte http://sqlfiddle.com/#!3/d178f/1/0
Reproduziu exatamente a mesma estrutura de banco de dados.
