请尝试使用ROW_NUMBER函数执行以下操作：
如果只想选择SEQ_NO作为新列，请执行以下操作：

WITH CTE AS
(
  SELECT *, ROW_NUMBER() OVER (PARTITION BY ID, SEQ_NO ORDER BY SEQ_NO) rn 
  FROM table_name
)
SELECT ID, SEQ_NO,
       CASE 
         WHEN rn>1 THEN
          CONCAT(CHAR(rn+63), CHAR(rn+63), SEQ_NO) 
         ELSE SEQ_NO
       END AS new_seq
FROM CTE 
WHERE rn <= 27
ORDER BY ID, new_seq

如果要更新SEQ_NO列，请执行以下操作：

WITH CTE AS
(
  SELECT *, ROW_NUMBER() OVER (PARTITION BY ID, SEQ_NO ORDER BY SEQ_NO) rn 
  FROM table_name
)
UPDATE CTE SET SEQ_NO = CONCAT(CHAR(rn+63), CHAR(rn+63), SEQ_NO) 

WHERE rn > 1 AND rn <= 27

请参见demo，其中一组数据的seq（01 - 10）重复三次。