How to show all data when using more than one parameter?

Question

Hi All,
I used a query like this to show the data in a report:
select col1, col2 // col1 and col2 are columns of tabale tab1
from tab1
where
tab1.col1 =
(case when :P_COL1 IS NOT NULL then // :P_COL1 IS A USER PARAMETER TO EQUAL COL1
:P_COL1 ELSE tab1.col1
end)
AND TAB1.COL3 =
(case when :P_COL3 IS NOT NULL then // :P_COL3 IS A USER PARAMETER TO EQUAL COL3
:P_COL3 ELSE tab1.col3
end)
The problem is when I run the report with paramters values or not, It shows the data which is not null for both col1 and col3.
That is when the value of col1 or col3 is null the report would not return that record!
I want the report to show all data not only values which is not null!
How to do this?

Answer 1

Rainer,
That where clause will fail when col1 in the table is null and the parameter has the dummy value. Consider the following:
variable p_col1 varchar2
exec :p_col1 := 'yourdummyvalue';
select
from
     select 'yourdummyvalue' col1 from dual
     union all
     select 'other' from dual
     union all
     select null from dual
     union all
     select 'X' from dual
) tab1
where nvl(tab1.col1,'yourdummyvalue') = nvl(nvl(:p_col1,tab1.col1),'yourdummyvalue')In this case, the query returns the row with null and the row with 'yourdummyvalue', where only the row with 'yourdummyvalue' should be returned.
You must do something like this:
where ( :p_col1 is null or ( :p_col1 = tab1.col1 ) )That one is the simplest and does not need a dummy value. Here are some other more complicated examples:
where nvl( :p_col1, 'yourdummyvalue' ) = decode( :p_col1, null, 'yourdummyvalue', tab1.col1 )or this:
where nvl( :p_col1, 'yourdummyvalue' ) = nvl2( :p_col1, tab1.col1, 'yourdummyvalue' )In the last 2 cases, it will not matter if the dummy value exists in the data, but they are unnecessarily complex.
Kurz