Alternate of using NVL with IN clause in Oracle 11g - sql

Question

I have a workplace problem to which I am looking for an easy solution.
I am trying to replicate it in a smaller scenario.
Problem in short
I want to use nvl inside an in clause. Currently I have an input string which consists of a name. It is used in a where clause like below
and column_n = nvl(in_parameter,column_n)
Now I want to pass multiple comma separated values in same input parameter. So if I replace = with in, and transpose the input comma separated string as rows, I cannot use the nvl clause with it.
Problem in Detail
Lets consider an Employee table emp1.
Emp1
+-------+-------+
| empno | ename |
+-------+-------+
| 7839 | KING |
| 7698 | BLAKE |
| 7782 | CLARK |
+-------+-------+
Now this is a simple version of an existing stored procedure
create or replace procedure emp_poc(in_names IN varchar2)
as
cnt integer;
begin
select count(*)
into cnt
from emp1
where
ename = nvl(in_names,ename); --This is one of the condition where we will make the change.
dbms_output.put_line(cnt);
end;
So this will give the count of number of employees passed as Input Parameter. But if we pass null, it will return the whole count of employee becuase of the nvl.
So these procedure calls will render the given outputs.
Procedure Call Output
exec emp_poc('KING') 1
exec emp_poc('JOHN') 0
exec emp_poc(null) 3
Now what I want to achieve is to add another functionality. So exec emp_poc('KING,BLAKE') should give me 2. So I figured a way to split the comma separated string to rows and used that in the procedure.
So if I change the where clause as below to in
create or replace procedure emp_poc2(in_names IN varchar2)
as
cnt integer;
begin
select count(*)
into cnt
from emp1
where
ename in (select trim(regexp_substr(in_names, '[^,]+', 1, level))
from dual
connect by instr(in_names, ',', 1, level - 1) > 0
);
dbms_output.put_line(cnt);
end;
So exec emp_poc2('KING','BLAKE') gives me 2. But passing null will give result as 0. However I want to get 3 like the case with emp_proc
And I cannot use nvl with in as it expect the subquery to return a single value.
1 way I can think of is rebuilding the whole query in a variable, based in input paramteter, and then use execute immediate. But I am using some variables to collect the value and it would be difficult to achieve it with execute immediate.
I am again emphasizing that this is a simple version of a complex procedure where we are capturing many variables and it joins many tables and has multiple AND conditions in where clause.
Any ideas on how to make this work.

Answer 1

This may help you
CREATE OR REPLACE PROCEDURE emp_poc2(in_names IN varchar2)
AS
cnt integer;
BEGIN
SELECT COUNT(*) INTO cnt
FROM emp1
WHERE
in_names IS NULL
OR ename IN (
SELECT TRIM(REGEXP_SUBSTR(in_names, '[^,]+', 1, level))
FROM dual
CONNECT BY INSTR(in_names, ',', 1, level - 1) > 0
);
dbms_output.put_line(cnt);
END;
Other way could be use IF ELSE or UNION ALL

Answer 2

If your real code is much more complex then your code readability might be greatly enhanced by using a proper collection type instead.
In the example below I have created an user defined type str_list_t that is a real collection of strings.
I also use common table expression (CTE) in the sql query to enhance the readability. In this simple example the CTE benefits for readability are not obvious but for all non-trivial queries it's a valuable tool.
Test data
create table emp1(empno number, empname varchar2(10));
insert into emp1 values(5437, 'GATES');
insert into emp1 values(5438, 'JOBS');
insert into emp1 values(5439, 'BEZOS');
insert into emp1 values(5440, 'MUSK');
insert into emp1 values(5441, 'CUBAN');
insert into emp1 values(5442, 'HERJAVEC');
commit;
Supporting data type
create or replace type str_list_t is table of varchar2(4000 byte);
/
Subprogram
create or replace function emp_count(p_emps in str_list_t) return number is
v_count number;
v_is_null_container constant number :=
case
when p_emps is null then 1
else 0
end;
begin
-- you can also test for empty collection (that's different thing than a null collection)
with
-- common table expression (CTE) gives you no benefit in this simple example
emps(empname) as (
select * from table(p_emps)
)
select count(*)
into v_count
from emp1
where v_is_null_container = 1
or empname in (select empname from emps)
;
return v_count;
end;
/
show errors
Example run
SQL> select 2 as expected, emp_count(str_list_t('BALLMER', 'CUBAN', 'JOBS')) as emp_count from dual
union all
select 0, emp_count(str_list_t()) from dual
union all
select 6, emp_count(null) from dual
;
EXPECTED EMP_COUNT
---------- ----------
2 2
0 0
6 6