Question : Return only rows that match

I would like to return all rows if an assignment_id is not entered
If a value is entered, only return the rows that match the entered assignment_id value
With the following query construct, if an assignment_id value is entered, it return the rows that matches the entered assignment_id and also rows that have a null assignment_id. How can I construct the query to return only the rows that matches the entered value or if null or <ALL> is entered return all personnel. We use a fuction to return a wildcard if <ALL> is entered.

SELECT DISTINCT emp_id,
p.emp_name,
p.ssn,
p.last_reviewed_date up_to_date,
p.dept,
cpp.assignment,
cpp.assignment_id
FROM personnel_vw p
INNER JOIN access_check_vw vw
ON p.dept_id = vw.dept_id
AND p.dept like '%VEHICLE2%'
AND p.active = 'Y'
AND (p.emp_status = 'PERMANENT' and p.assignment_type = 'SALES')
AND vw.pw_id = '111'
INNER JOIN chk_per_unit_vw cpu
ON p.emp_id = cpu.emp_id
AND cpu.unit_id LIKE get_decode_null('<ALL>') -- Function - If <ALL> decodes to %, if not, decodes to the entered value
LEFT JOIN chk_per_assignments_vw cpp
ON p.emp_id = cpp.emp_id
AND nvl(cpp.assignment_id,'%') LIKE get_decode_all('10930') -- Function - If <ALL> decodes to %, if not decodes to the entered value

Answer : Return only rows that match

I think I understand what you are after. See if this helps.

It was all executed using SQL*Plus.

                       
         
           
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             drop table tab1 purge;
create table tab1(col1 varchar2(10));

insert into tab1 values('Hello');
insert into tab1 values('World');
commit;


var myVar varchar2(10)
--entered 'll'
exec :myVar := 'll';
select * from tab1 where col1 like '%' || decode(:myVar,'<ALL>',null,:myVar) || '%';

--entered null
exec :myVar := null;
select * from tab1 where col1 like '%' || decode(:myVar,'<ALL>',null,:myVar) || '%';


--entered '<ALL>'
exec :myVar := '<ALL>';
select * from tab1 where col1 like '%' || decode(:myVar,'<ALL>',null,:myVar) || '%';

           
         