I have two datasets that needs to be merged. But one row in the main dataset is representing multiple row in the secondary dataset.

Data set 1
Barcode SEQ ITEM NO REC NO FGROUP GRAMAMOUNT RECORDID AMOUNT UNIT
A11 1 1 0 01.01.02 30 QP112 30 g
A11 2 1 0 04.02.01 23 RE3421 15 ml
A11 1 2 1 99.99.99 0 50 %
P12 1 1 1 12.04.11 12 A120 12 g
Data set 2
Barcode SEQ REC NO FGROUP GRAMAMOUNT RECORDID AMOUNT UNIT
A11 1 1 20.01.02 1.2 CS 1.2 g
A11 1 1 12.02.01 63 PW145 60 ml
A11 1 1 03.03.01 12 K102 10 ml

I would need to merge data set 2 into data set 1 by matching the barcode, seq and rec no.
In this instance the item in the third row matches all the items in data 2 and that is what I need, for 1 row in dataset 1 to be populated by all three rows in the merged data set.

So the merged dataset should look like this
Barcode SEQ ITEM
NO		 REC NO FGROUP GRAMAMOUNT RECORDID AMOUNT UNIT
A11 1 1 0 01.01.02 30 QP112 30 g
A11 2 1 0 04.02.01 23 RE3421 12 ml
A11 1 2 1 20.01.02 0.6 CS 0.6 g
A11 1 2 1 12.02.01 31.5 PW145 30 ml
A11 1 2 1 03.03.01 6 K102 5 ml
P12 1 1 1 12.04.11 12 A120 12 g
So it's really appending plus merging at the same time. Does anyone have any idea how I can do so?
And if the amount and unit in data set 1 is for example 50% then what is being populated in merged dataset will show 50% of the value in data set 2.

Will I be better off to append than to merge?

Thank you very much.

Nan Xin