How to group by two columns in mysql

Question

I am building a chat website, I have a table that contains the following columns, from_id , to_id , messages .

The from_id is the id of the user that the chat is from and the to_id is the id of the user the chat is sent to.

Now I want to get all the chats but I also want to group it in such a way that if the to_id is my id, it will group it by from_id and if the from_id is my user id, then it will group it by to_id , I tried this SELECT * FROM chats WHERE from_id=:me || to_id=:me GROUP BY from_id, to_id SELECT * FROM chats WHERE from_id=:me || to_id=:me GROUP BY from_id, to_id but it only group it when the from_id and the to_id are the same, how can I also make it go the other way round too

Answer 1

Aggregation is normally used to take multiple rows and to condense them into a single row. That does not seem to be your intentionl

It sounds like you have an ordering problem, not an aggregation problem. If you want to order the chats by the "other" id, you can use:

select c.*
from chats c
where :me in (to_id, from_id)
order by (case when :me = to_id then from_id else to_id end);

Answer 2

You can do it with a CASE expression:

SELECT CASE WHEN from_id = :me THEN to_id ELSE from_id END id,
       GROUP_CONCAT(messages) messages -- I added this as an aggregate function
FROM chats 
WHERE :me IN (from_id, to_id) 
GROUP BY id

But if you don't need any aggregation, then you should not use GROUP BY , but DISTINCT :

SELECT DISTINCT CASE WHEN from_id = :me THEN to_id ELSE from_id END id
FROM chats 
WHERE :me IN (from_id, to_id)