Multiple rows values to one cell in MySQL

Question

I would like to ask for your help in order to achieve the following I have a table that the id column may have the same id on multiple rows which corresponds to different values on another column like the example bellow

TABLE #1

+-----+---------+
| id1 | value1  | 
+-----+---------+
|  1  |    1    | 
+-----+---------+
|  1  |    2    | 
+-----+---------+
|  1  |    3    | 
+-----+---------+
|  2  |    4    | 
+-----+---------+
|  2  |    5    | 
+-----+---------+
|  2  |    6    | 
+-----+---------+

Based on id column I need the values that corresponds to the same id to be inputted in the same cell separated by a comma like the following example

Those need to be updated on another table

TABLE #2

+-----+---------+
| id2 | value2  | 
+-----+---------+
|  1  |  1,2,3  | 
+-----+---------+
|  2  |  4,5,6  | 
+-----+---------+

How can this be done?

Answer 1

What is the reason for denormalizing your data and violating First Normal Form (1NF)? You shouldn't do that - it's better to have the data normalized. You could create a view if it's required to present data this way.

---

Anyways, since this answer should also include a solution, here's one:

Use GROUP_CONCAT() aggregate function:

SELECT id1, GROUP_CONCAT(value1 ORDER BY value1 ASC SEPARATOR ',')
FROM table1
GROUP BY id1

To update results in other table where ids match:

UPDATE table2 a
INNER JOIN ( 
  SELECT id1, GROUP_CONCAT(value1 ORDER BY value1 ASC SEPARATOR ',') AS value2
  FROM table1
  GROUP BY id1
  ) b ON a.id1 = b.id2
SET a.value2 = b.value2