How Can I Control the Order of Values in MySQL's GROUP_CONCAT Function?

Order Results in GROUP_CONCAT

When using the GROUP_CONCAT function to combine values for grouped rows, it can be useful to maintain the order of these values.

Problem: Unordered Results

Suppose we have a table named "li" with columns: client_id, views, and percentage. We want to group the rows by client_id and concatenate the views values. We initially try the following:

SELECT li.client_id,
       group_concat(li.views) AS views,
       group_concat(li.percentage) FROM li
       GROUP BY client_id;

This produces results with the views concatenated, but in an arbitrary order:

+-----------+-------------------+-----------------------------+
| client_id | views             | group_concat(li.percentage) |
+-----------+-------------------+-----------------------------+
|         1 | 6,4,9,2,7,5,3,8,1 | 20,55,56,67,80,66,33,34,52  |
+-----------+-------------------+-----------------------------+

Solution: Order Within GROUP_CONCAT

To order the results within the GROUP_CONCAT, we can use ORDER BY inside the function:

SELECT li.client_id,
       group_concat(li.views ORDER BY li.views ASC) AS views,
       group_concat(li.percentage ORDER BY li.views ASC) AS percentage
       FROM li
       GROUP BY client_id

This will order the views column in ascending order, while maintaining the corresponding percentage values in the same order:

+-----------+-------------------+----------------------------+
| client_id | views             | percentage                 |
+-----------+-------------------+----------------------------+
|         1 | 1,2,3,4,5,6,7,8,9 | 52,67,33,55,66,20,80,34,56 |
+-----------+-------------------+----------------------------+

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