Find and add missing value

[moomphas]

Hi,

I'm looking for a way to automatically add X5 xxx and X6 xxx from the second table to the first table. Basically it's about looking for missing IDs and adding them under last entry in the first table. Any ideas?

ID	Header		ID	Header
X1	aaa		X1	xxx
X2	aaa		X1	xxx
X3	aaa		X4	xxx
X4	aaa		X3	xxx
			X2	xxx
			X5	xxx
			X1	xxx
			X6	xxx

Expected result:

ID	Header
X1	aaa
X2	aaa
X3	aaa
X4	aaa
X5	xxx
X6	xxx