Concat rows based on condition [duplicate]

Question

I'm working with a table that has values like this

ID	Name	Value
123	Size	1
123	Size	2
123	Size	3
123	Type	Shoes
234	Size	6
234	Size	7
234	Type	Shirt

I want to CONCAT the answers if the name = size. So, I'd love to do this:

ID	Name	Value
123	Size	1, 2, 3
123	Type	Shoes
234	Size	6, 7
234	Type	Shirt

My thought was to use a case when size = 'name' then concat? But I'm not sure if this is the correct use. Thank you so much.

Answer 1

You can use string_agg:

SELECT id, name, string_agg(value, ',')
  FROM a
 GROUP BY id, name
 ORDER BY 1,2

Output:

ID	Name	value
123	Size	1,2,3
123	Type	Shoes
234	Size	6,7
234	Type	Shirt

Here is a dbfiddle showing how it works. This is assuming that there is only one column with name = Type, if there are more this will merge those too.