Oracle 11g Release 2

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SELECT REGEXP_REPLACE(
         'abc#95988287?3008009095',
         '\?\d'
       ) AS replaced_value
FROM   DUAL;


REPLACED_VALUE


abc#95988287008009095


SELECT REGEXP_REPLACE(
         'abc#95988287?3008009095',
         '\?\d+'
       ) AS replaced_value
FROM   DUAL;


REPLACED_VALUE


abc#95988287


SELECT REGEXP_SUBSTR(
         'abc#95988287?3008009095',
         '#(\d+)\?',
         1,
         1,
         NULL,
         1
       ) AS replaced_value
FROM   DUAL;


REPLACED_VALUE


95988287


SELECT REGEXP_REPLACE(
         'abc#95988287?3008009095',
         '.*?#|\?\d+'
       ) AS replaced_value
FROM   DUAL;


REPLACED_VALUE


95988287