Adding Match to a formula and unique list in dropdown box

Hi,

Can anyone help with the two requirements listed below please.

On the Journal sheet in cell I6 I would like a list which will only display unique dates based in column K of the data 2 tab. How do I do this?

Then the second requirement is to amend the formulas currently on the summary sheet. Currently it is return all data from “data 2” sheet howeverwhat I would like is that if there is da date in cell I6 for it only to pull data based on the match.

e.g. if I6 is blank then return everything
e.g. 2 If I6 contains 25/5/2015 then it would match this with column K of the data sheet and return the values 396 and 197 only.

Can anyone help with either please?