compare user supplied list against table, with nulls for non-matching rows - sql

Question

Given a list of user-supplied numbers, which I'll refer to as myList, I want to find out which ones have a match against table MasterList, and which ones are null (no match)
so, given db contents
MasterList
----------
ID Number
1 3333333
2 4444444
3 5555555
If myList is ['1111111','2222222','3333333','4444444']
I want the following output:
1111111, null
2222222, null
3333333, 1
4444444, 2
Ideas I've tried:
This, of course, yields only the ones that match.
select Number, ID
from MasterList
where Number in('1111111','2222222','3333333','4444444')
My next idea is no more helpful:
select temp.Number, master.Number
from MasterList master
left join MasterList temp
on master.id=temp.id
and temp.Number in('1111111','2222222','3333333','4444444')
If the list were itself a table temp, it would be trivial to get the desired output:
select temp.number, master.id
from temp -- (ie, the list, where temp.number is the given list)
left join master on master.number=temp.number
-- optional where
where temp.number in('1111111','2222222','3333333','4444444')
This idea never materialized:
select temp.number, master.id
from (select '1111111','2222222','3333333','4444444') temp
left join master on master.number on....
Can this be done without a temporary table?
If not, how do you make a temporary table in DB2? (IBM documentation is helpful if you already know how to do it...)

Answer 1

You want an outer join, here a left outer join (we want all the rows from the left and any rows on the right that match the join condition), as you rightly say in the question. Here I'm using a Common Table Expression (CTE) to basically create a temp table on the fly.
WITH inlist (num) as ( VALUES
(111111),
(222222),
(333333),
(444444) )
SELECT num, id
FROM inlist LEFT OUTER JOIN masterlist
ON masterlist.number = inlist.num
ORDER BY num;
That yields:
NUM ID
----------- -----------
111111 -
222222 -
333333 1
444444 2
4 record(s) selected.

Answer 2

I'm not super-familiar with DB2 (haven't written SQL for that in at least 15 years, and not much back then), so I don't know how much you'll need to edit this to make it work, but I think this will do what you want (Edited SQL to use VALUES clause):
SELECT
my.Number1,
CASE WHEN ml.Number1 IS NULL
THEN NULL
ELSE ROW_NUMBER() OVER (ORDER BY my.Number1) END AS Indicator
FROM
(VALUES ('1111111'),('2222222'),('3333333'),('4444444'))
AS my(Number1)
LEFT JOIN
MasterList AS ml
ON
my.Number1 = ml.Number1;