SQL> select to_number(8.91e+10 ,'999999999999') from dual;

TO_NUMBER(8.91E+10,'9999999999
------------------------------
                   89100000000

SQL> select to_char(8.91e+10) from dual;

TO_CHAR(8.91E+10)
-----------------
89100000000

------解决方案--------------------
给你个例子：
SQL code
SQL> CREATE TABLE TEST_ZZ (SID NUMBER);

Table created

SQL> INSERT INTO TEST_ZZ VALUES(11111111111111111111111);

1 row inserted

SQL> COMMIT;

Commit complete

SQL> SELECT * FROM TEST_ZZ;

       SID
----------
1.11111111

SQL> SELECT TO_CHAR(SID,'999999999999999999999999999') FROM TEST_ZZ;

TO_CHAR(SID,'99999999999999999
------------------------------
     11111111111111111111111

SQL>