如果您想删除下划线，那么replace可能比substr + instr组合更好。

SQL> with test (col) as
  2    (select 'SE8000901008' from dual union all
  3     select 'SE8000901008_' from dual
  4    )
  5  select col,
  6    replace(col, '_') result
  7  from test;

COL                            RESULT
------------------------------ ------------------------------
SE8000901008                   SE8000901008
SE8000901008_                  SE8000901008

SQL>

您可以检查是否有任何underscre，并选择其他选项

with test (col) as
    (select 'SE8000901008' from dual union all
     select 'SE8000901008_' from dual
    )
SELECT
CASE WHEN INSTR(col, '_') > 0 then
  SUBSTR(col, 1, INSTR(col, '_') -1 )
ELSe col
ENd IF
FROM test

| 中频|
| - ------|
| SE8000901008|
| SE8000901008|
fiddle