Combine data from several columns into one while removing duplicate values - with formula

[Bookender]

Okay, so, I have a problem that has caused a bit of hair-pulling on my side, especially as all I have been able to Google results for is how to concatenate two cells with an ampersand:

Basically, I have three columns, A, B and C. These columns will contain variable amounts of data, based on the data in an entirely different sheet (which is updated every two hours, hence why I want this bit to run without any input outside of opening the sheet), and the quantity of data in each column can vary from 1 to 260 rows.

[TABLE="class: grid, width: 200"]
<TBODY>[TR]
[TD]A
[/TD]
[TD]B
[/TD]
[TD]C
[/TD]
[/TR]
[TR]
[TD]1
[/TD]
[TD]2
[/TD]
[TD]5
[/TD]
[/TR]
[TR]
[TD]2
[/TD]
[TD]3
[/TD]
[TD]6
[/TD]
[/TR]
[TR]
[TD]3
[/TD]
[TD]4
[/TD]
[TD]7
[/TD]
[/TR]
[TR]
[TD]5
[/TD]
[TD]5
[/TD]
[TD][/TD]
[/TR]
[TR]
[TD][/TD]
[TD]7
[/TD]
[TD][/TD]
[/TR]
</TBODY>[/TABLE]



What I want is to end up with a single column D with all of unique values from A, B and C (column D doesn't have to be in order; this is just to help demonstrate what I want):

[TABLE="class: grid, width: 100"]
<TBODY>[TR]
[TD]D
[/TD]
[/TR]
[TR]
[TD]1
[/TD]
[/TR]
[TR]
[TD]2
[/TD]
[/TR]
[TR]
[TD]3
[/TD]
[/TR]
[TR]
[TD]4
[/TD]
[/TR]
[TR]
[TD]5
[/TD]
[/TR]
[TR]
[TD]6
[/TD]
[/TR]
[TR]
[TD]7
[/TD]
[/TR]
</TBODY>[/TABLE]

Anyone got ideas for how I can construct my formula for this?

(I got Excel 2010, btw)

 

[vllgv]

This link shows 3 ways it can be done.

How to extract unique values from multiple columns in Excel?