Excel 2007 : lookup table based attribute generation

My problem is this:
I have 2 tables. One of them has n randomly distributed rows having for the attribute 'X'.
Second table maps each unique row attribute 'X' to a value of an attribute 'Y'.

So, how should I add an attribute in the first table that has the corresponding 'Y' values.

Thanks

Hi,
as far as I can understand what you need , something like a VLOOKUP function might help