如何判断一个字符串是否为数字或日期?

SQL> CREATE OR REPLACE FUNCTION is_number (parmin VARCHAR2)
2 RETURN NUMBER
3 IS
4 val NUMBER;
5 BEGIN
6 val := TO_NUMBER (NVL (parmin, 'a'));
7 RETURN 1;
8 EXCEPTION
9 WHEN OTHERS
10 THEN
11 RETURN 0;
12 END;
13 / Function created. SQL> select is_number('a') from dual; IS_NUMBER('A')
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0 SQL> select is_number('0.998') from dual; IS_NUMBER('0.998')
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1 SQL> select is_number('9999999999999999') from dual; IS_NUMBER('9999999999999999')
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1

SQL> CREATE OR REPLACE FUNCTION is_date (parmin VARCHAR2)
2 RETURN NUMBER
3 IS
4 val DATE;
5 BEGIN
6 val := TO_DATE (NVL (parmin, 'a'), 'yyyy-mm-dd hh24:mi:ss');
7 RETURN 1;
8 EXCEPTION
9 WHEN OTHERS
10 THEN
11 RETURN 0;
12 END;
13 /
Function created.
SQL> select is_date('a') from dual; IS_DATE('A')
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0 SQL> select is_date('2004-05-05') from dual; IS_DATE('2004-05-05')
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1 SQL> select is_date('2004/01/01') from dual; IS_DATE('2004/01/01')
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1 SQL> select is_date('01/01/04') from dual; IS_DATE('01/01/04')
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1 SQL> select is_date('01-jan-04') from dual; IS_DATE('01-JAN-04')
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1