Vlookup and Concatenate

Hi All,

I have been trying to concatenate data from the same column by looking up and matching the IDs from two different sheets, but I have had any luck with the formula. Keeps giving me an error.

I have attached an excel document as an example.

What I would like to do is match the ID from Sheet1 Column A with the ID on Sheet2 Column A and Concatenate cells from Sheet2 Column B that pertain to that ID.

It sounds like a simple formula but I think I am over complicating it.

Thanks!

Column A in Sheet2 has duplicate values. So for example ID# 678584 is twice and has two (2) different values for Demo ID.
I would like to look up ID in A Sheet1, see if it exists in A SHeet2 and if so bring back the values that exist in B-Sheet2. ( Since there are more than 1 value on column B sheet2 I figured the concatenate function could work)

Hi,
I have used that formula before and it works but where I am having difficulties is how to bring back multiple values in one cell. So since an ID has more than Demo ID, I need to bring back all of the DEMO IDs associated to that particular ID. I figured Concatenate formula would work but now that I think about it, an array formula could work better.

Example:
Sheet1
A2- 12345
A3- 67899
A4- 23456
A5- 45677

Sheet2:
A2-12345 B2 - John
A3 - 12345 B3-Smith
A4-45677 B4 - Dan
A5-67899 B5-Joe
A6-45677 B6- Bill
A7-23456 B7- James
A8-23456 B8- Dennis

So, Sheet1 has unique values and Sheet2 contains duplicate IDs which I do not want to filter. Column B on Sheet2 has the values associated to that particular ID.
I would like to bring back the values that are on column B sheet2 to Sheet1 by matching the IDs. B2 in Sheet1 should look something like this....

A2- 12345 B2 -John,Smith
A3- 67899 B3-Joe
A4- 23456 B4- James, Dennis
A5- 45677 B5 - Dan, Bill