1 step
- in DataModel->UserParameters u should create user parameter:
for examp. NB_OF_REPORT (type number)
2 step (depend from your startup procedure :
-- if u use parameter form :
--- create parameter form, in parameter form create field (with any names) and link this field with :NB_OF_REPORT parameter
(in this case had better for u - set type of field in parameter form - static list and type values (1,2,3,4) )
-- if u use RUN_PRODUCT(...) u should add new parameter in paramer_list
NB_OF_REPORT as text parameter and set needed value
-- if u use command line then :
runrep usr/pwd@db .... NB_OF_REPORT=2 (for example)

3. little change query:

select ENAME col from emp Where job = ‘ANALYST’
AND :NB_OF_REPORT = 1
union
select to_char(SAL, '99999.99') col from emp Where job = ‘ANALYST’;
AND :NB_OF_REPORT = 2
union
select to_char(HIREDATE,'mm/dd/rrrr') col from emp Where job = ‘ANALYST’
AND :NB_OF_REPORT = 3
union
select to_char(EMPNO) col from emp Where job = ‘ANALYST’
AND :NB_OF_REPORT = 4

lood luck.