对当前排序使用ROW_NUMBER()窗口函数对行进行初始排序。
然后创建3组行：顶部的行、'item5'的行和'item5'以下的行将与UNION ALL组合并按组和行号排序：

WITH cte AS (
    SELECT *, 
           ROW_NUMBER() OVER (ORDER BY CASE id WHEN 'item0' THEN 0 WHEN 'item1' THEN 1 ELSE 2 END, name) AS rn
    FROM tablename
)  
SELECT id, name
FROM (
  SELECT * FROM (SELECT *, 1 grp FROM cte WHERE id <> 'item5' ORDER BY rn LIMIT 5)
  UNION ALL
  SELECT *, 2 FROM cte WHERE id = 'item5'
  UNION ALL
  SELECT * FROM (SELECT *, 3 FROM cte WHERE id <> 'item5' ORDER BY rn LIMIT -1 OFFSET 5) -- negative limit means there is no limit
)
ORDER BY grp, rn;

请注意，代替：

ORDER BY CASE id WHEN 'item0' THEN 0 WHEN 'item1' THEN 1 ELSE 2 END, name

您可以用途：

ORDER BY id = 'item0' DESC, id = 'item1' DESC, name

参见简化的demo。