Searching For Differences Between Columns

I've got a spreadsheet which lists reference numbers and a value of each one on for two different weeks which looks like this (please ignore the ....'s - I was trying to illustrate the colums clearly but the spaces seem to get removed when I post this)

ref(week 1):...........Value (week 1):......ref (week 2):....Value (week 2):
123456...................£100.23...............123456.............£100.23
113456...................£123.45...............147258.............£75.32
147258...................£74.25.................978645.............£1000.02

What I want to do is compare the value for week 1 and week 2 for each reference number. The problem is that not all the reference numbers for week 1 will be in week 2, and not all the reference numbers in week 2 will have appeared in week 1. I would like to know if there's a way that excel can identify a specific reference number, search for the values for this in week one and week two, and display any differences between these, (e.g. on the above spreadsheet I would like to identify that ref 123456 appears in both weeks and that the balance is the same, reference 147258 appears in both but the value is different, and that reference 113456 & reference 978645 do not appear in both weeks).