Merging two worksheets and setting a migration date

[bmas56]

Related to my first post (for which I thank JeffreyBrown, see
http://www.excelforum.com/excel-gene...ing-names.html for the context), I am now looking for another capability, which I anticipate using often.

In the first instance of it, I want to match names in two work sheets and enter a "migration date" in the first sheet that comes from the second sheet. One wrinkle: there are already plenty of dates listed in the first sheet. The dates from the second sheet may override the dates in the first sheet, but if there is not a matching name in the second sheet, any other date related data needs to remain instact. For example, if I have a name Vince Wilfork in the first sheet and the second sheet, and on the second sheet, I have Vince listed to migrate on 6/21/2011, that data should be inserted by the procedure onto the first sheet.

If there are no matching dates on the second sheet, then no value should be inserted or modified on the first sheet, because some dates are already filled in.

Is there a function, a group of functions, or a simple macro to do this? - and it would be great if it could be a function or macro that could be applied to the entire worksheet because it is 18-20,000 records long, has sparse data entered in some of these fields already, so "going to the bottom of the column" doesn't always work.

Once again, I appreciate the help that I've already been given by Jeff; hopefully I can get fairly quick turnaround on this one; I am thankful for what's already been shared, and I'll be thankful for helpful tips once again. ---Brian