Question

I have the following table

ID | tbl | reply |   time
--- ----- ------- -----------
1  | blue|   0   |   01:00
--- ----- ------- -----------
2  | red |   1   |   01:05
--- ----- ------- -----------
3  | pink|   1   |   11:11
--- ----- ------- -----------
4  | pink|   0   |   22:22
--- ----- ------- -----------
5  | pink|   4   |   00:03
--- ----- ------- -----------

The reply refers to the ID column so ID and reply have a connection. ID is the parent of reply. When reply=0 then it means that we have selected a parent row else it is just the reply.

At the moment I have this simple mysql query in order to select only the parents

SELECT tbl, time FROM table WHERE reply=0 ORDER BY time ASC 

Which will select first the ID=1 and then the ID=4

What I want is to be able to ORDER the parents by the time of the childrens but not to show the childrens. So in the above example just because ID=5 has a time of 0:03 then the ID=4 should appear first and then ID=1

Any ideas how to do this except from creating another table?
If it is better maybe any php ideas on how to do this?

Thank you very much

Answer 1

My SQL is a bit rusty, but:

SELECT t.tbl, t.time 
FROM table t 
WHERE t.reply=0 
ORDER BY 
(SELECT MAX(time) FROM table WHERE reply = t.id) DESC,
t.time DESC

The trick is to give the main query table a name (t in this example) – you can then reference it in the subquery without the server getting confused.

I know this might just be your example, but you’d be best storing your time column as a DATETIME or even a UNIX timestamp (in an INT field). You’ll need the date, so that something posted yesterday at 23:00 isn’t seen as more recent than something posted today at 15:00