How to Sort Values Within a GROUP_CONCAT String in MySQL?

Sorting GROUP_CONCAT Values in MySQL

In the realm of MySQL, you may encounter the need to manipulate data returned from a GROUP_CONCAT statement. One common requirement is to sort the values within the concatenated string.

To achieve this, you can leverage the GROUP_CONCAT function's hidden gem: the ORDER BY clause. By adding an ORDER BY clause to the subquery within the GROUP_CONCAT, you can sort the values before they are concatenated.

For example, consider the following query:

GROUP_CONCAT((SELECT GROUP_CONCAT(parent.name SEPARATOR " » ") 
FROM test_competence AS node, test_competence AS parent 
WHERE node.lft BETWEEN parent.lft AND parent.rgt 
  AND node.id = l.competence 
  AND parent.id != 1 
ORDER BY parent.lft) SEPARATOR "<br />\n") AS competences

This query returns rows with the concatenated values of the parent.name column, sorted in ascending order based on the parent.lft column.

However, if you desire a specific order, such as descending order, simply adjust the ORDER BY clause:

... ORDER BY parent.lft DESC

It's worth noting that the ORDER BY clause in GROUP_CONCAT is only applicable to the innermost subquery. If you have a multiple-layer subquery, the outer queries will not be affected by the ORDER BY clause.

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