如何排序，mysql中的一个json_object

Question

I've a problem sorting a JSON_OBJECT:

How can I sort the objects as they are in the JSON OBJECT?

Answer 1

You can't control the order of the elements in the array that json_arrayagg() generates, even in MySQL 8.0, as explained in the documentation :

Aggregates a result set as a single JSON array whose elements consist of the rows. The order of elements in this array is undefined.

An ugly and not scalable work around is to use group_concat() to manually generate the json array:

select 
    dashboard,
    widget,
    ...
    concat(
        '[',
        group_concat(
            json_object('color_mode', color_mode, ...)
            order by <your_ordering_clumn>
        ),
        ']'
    ) js_array
from datadog_wigets_markers 
group by dashboard, widget, ...

This will fail on long json strings. I would rather try and live with json_arrayagg() and unordered arrays.

Side note: you should enumerate all the non-aggregated columns in the group by clause; it's a requirement in most databases, and a good coding practice.

Answer 2

@Gordon Linoff 在这篇文章中的回答在 MySQL 8.0 上对我有用，但我没有测试它的可扩展性。