mysql multiple values in 1 row

Question

I have this table units

id	value
1	value 1
2	value 2
3	value 3

and another table called users

id_units	concat_value
1,2	---
1,3,2	---

what I'm struggling with is how can I show on the concat_value column all the values separated by comma for each of the ids on the id_units field?

I need it to look like this

id_units	concat_value
1,2	value 1,value2
1,3,2	value 1,value3,value2