GROUP_CONCAT change GROUP BY order

Question

I have a VIEW (lots of joins) that outputs data ordered by a date ASC. Works as expected.

OUTPUT similar to:

ID date         tag         


        

Answer 1

That is because mysql does not guarantee what exact rows will be returned for the fields that are not used in aggregation functions or wasn't used to group by.

And to be clear "mature" rdbms (such as postgre, sql server, oracle) do not allow to specify * in GROUP BY (or any fields without aggregation or that was not specified in GROUP BY) - and it is great "limitation".