Assinging default values when nothing input to varibale by user.

Question

Hello I need to right a script that will ask for 2 date ranges to be specified by the user, this script should default to the earliest and most recent date in a table if the user dosent enter anything for each value. My script will be something like this
SELECT *
FROM table1
WHERE order_date BETWEEN &var1 AND &var2
I tried using define to give the variables an initial value but instead the script uses that value and dosent ask for input. Is it possible to use varibales this way and if so then how can I do it.
Thanks
Mike

Answer 1

Consider this,
SQL> create or replace function maxdate return date is
2 lv_dt date;
3 begin
4 select max(hiredate)
5 into lv_dt
6 from emp;
7 return lv_dt;
8 end;
9 /
Function created.
SQL> ed
Wrote file afiedt.buf
1 create or replace function mindate return date is
2 lv_dt date;
3 begin
4 select min(hiredate)
5 into lv_dt
6 from emp;
7 return lv_dt;
8* end;
SQL> /
Function created.
SQL> select mindate, maxdate from dual;
MINDATE MAXDATE
17-DEC-80 23-MAY-87
SQL> select * from emp
2 where hiredate between nvl('&H1', mindate) and NVL('&H2', maxdate);
Enter value for h1:
Enter value for h2:
old 2: where hiredate between nvl('&H1', mindate) and NVL('&H2', maxdate)
new 2: where hiredate between nvl('', mindate) and NVL('', maxdate)
EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO
7369 SMITH CLERK 7902 17-DEC-80 800 20
7499 ALLEN SALESMAN 7698 20-FEB-81 1600 300 30
7521 WARD SALESMAN 7698 22-FEB-81 1250 500 30
7566 JONES MANAGER 7839 02-APR-81 2975 20
7654 MARTIN SALESMAN 7698 28-SEP-81 1250 1400 30
7698 BLAKE MANAGER 7839 01-MAY-81 2850 30
7782 CLARK MANAGER 7839 09-JUN-81 2450 10
7788 SCOTT ANALYST 7566 19-APR-87 3000 20
7839 KING PRESIDENT 17-NOV-81 5000 10
7844 TURNER SALESMAN 7698 08-SEP-81 1500 0 30
7876 ADAMS CLERK 7788 23-MAY-87 1100 20
EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO
7900 JAMES CLERK 7698 03-DEC-81 950 30
7902 FORD ANALYST 7566 03-DEC-81 3000 20
7934 MILLER CLERK 7782 23-JAN-82 1300 10
14 rows selected.