Hello Everyone,
I'm not sure what function to use to accomplish this;

I have 4 columns;
A B C D
OLD ID ID REF LIST NEW ID RETURN VALUE
01224 01224 1 1
01225 01225 2 2
01226 01226 3 3
01227 01227 4 4
01227 01228 5 4
01227 01229 6 4
01228 01230 7 5
01228 01231 8 5
01229 01232 9 6
Column A is an old list of ship to address IDs for our customers. Each
customer can have more than one ship to address, hence the multiple ship to
IDs.

Column B is just a reference list of customer IDs. Its used to match the
old list of customer ship to ids in column A to the new ship to ids in
column C. Example; old id 01224 is now new id 1, old id 01225 is now new id 2
and so on.

What I need is a formula/function that looks at the numbers in column A and
then determines if theres a matching number anywhere in column B. If the
value in A1 = a value in B1:B5, then I want the formula to return the
matching value in column C to column D.(see example above for desired result)

I need to come up with some type of formula/function, because I have over
10,000 old IDs in a list to change into new IDs and don't want to have to
to this line by line.

Thanks for any help or alternative suggestions you may have.