How to create a dynamic where clause in oracle - oracle11g

Question

My requirement is to create a procedure or SQL query in which where clause should be created in run time depending on the paramters provided by the user.
Example if user provides data for three columns then where clause should have filter conditions for these three columns only to select the data from database table, like wise if user provides data for 4 columns then where caluse should have 4 columns.

Answer 1

I don't see any very specific solution to your question but it can be done using putting OR in where clause with different set of user input. See below:
Created procedure: Here my employee table has emp_id,name and salary columns. Now am assuming user sometimes passes emp_id and emp_name alone.
CREATE OR REPLACE PROCEDURE dynmc_selec (id NUMBER DEFAULT 0,
name VARCHAR2 DEFAULT 'A',
salary NUMBER DEFAULT 0,
emp_output IN OUT SYS_REFCURSOR)
AS
var VARCHAR2 (100);
BEGIN
--You need to make several combinations in where clause like ( emp_id , emp_name , salary ) OR ( emp_id , emp_name ) OR (emp_name , salary ) and use it in where clause with 'OR'.
--Also its needed that all the columns of the table is in where clause. If user doesnot pass anything then defualt value will be passed.
var :=
'select emp_id from employee where ( emp_id ='
|| id
|| ' and emp_name = '''
|| name
|| ''' ) OR emp_sal = '
|| salary;
DBMS_OUTPUT.put_line (var);
EXECUTE IMMEDIATE var;
OPEN emp_output FOR var;
EXCEPTION
WHEN OTHERS
THEN
NULL;
END;
Calling it:
declare
a SYS_REFCURSOR;
v_emp_id employee.emp_id%type;
begin
--passing emp_id and name only
dynmc_selec(id=>1,name=>'KING',emp_output=>a);
loop
FETCH a INTO v_emp_id;
EXIT WHEN a%NOTFOUND;
DBMS_OUTPUT.PUT_LINE(v_emp_id );
end loop;
end;
Output:
select emp_id from employee where ( emp_id =1 and emp_name = 'KING' ) OR emp_sal = 0
1

Answer 2

select * from test_table
where
(1 = nvl2(:l_date, 0, 1) or created_at > :l_date)
and (1 = nvl2(:l_no, 0,1) or no = :l_no);
With Oracle nvl2 function:
When the parameter l_date is null, then 1 = nvl2(l_date, 0, 1) evaluates to true and the filter by created_at is not taking place.
When the parameter l_date is not null, then 1 = nvl2(l_date, 0, 1) evaluates to false and the filter by created_at is taking place.
The same thing happens with the parameter l_no.