mysql：非分组项目在使用分组依据时崩溃

Question

Problem: I am currently grouping a table in mysql by one column and this will collapse other columns to one row for each group.
How can I control which row will be displayed after the group by?
For example, for one of the columns I would like to sort it and then have only the top column in each group be displayed.

Answer 1

Most cases where this comes up, you don't really want aggregation. You want to filter the data. So, say you have a bunch of records for entities that are updated over time. If you want the most recent row for each entity, you can use:

select t.*
from t
where t.created_at = (select max(t2.created_at) from t t2 where t2.entity_id = t.entity_id);

However, the correct thing for you to do is probably to delete this question. Ask another question with sample data, desired results, and the query that you are using.