Question

I want to generate a thread-like view

In the table I have from,to,date and some other columns

I want to output the rows grouped by from AND to

example data in DB

from,to,date
a,b,somedate
a,c,somedate
b,a,somedate

Query:

SELECT 
    from, to, date 
FROM 
    data 
GROUP BY 
    from, to 
ORDER BY 
    date DESC;

The output I expect is like this: (where from and to is grouped together)

a,b,somedate
a,c,somedate

(b,a,somedate not shows because its in the a,b group) 

but it doesn’t ..

The general idea is to have a Messaging View “by user” ..
where the list is sorted by recipients,date (not by message) …

Answer 1

If you want one row returned for every (from, to) combination:

SELECT one, two, MIN(somedate) 
FROM
( SELECT `from` AS one, `to` AS two, somedate 
  FROM data 
  WHERE `from` <= `to`
UNION ALL
  SELECT `to`, `from`, somedate 
  FROM data 
  WHERE `from` > `to`
) AS tmp
GROUP BY one
       , two
ORDER BY one
       , two

or, if you want all records:

SELECT one, two, somedate 
FROM
( SELECT `from` AS one, `to` AS two, somedate 
  FROM data 
  WHERE `from` <= `to`
UNION ALL
  SELECT `to`, `from`, somedate 
  FROM data 
  WHERE `from` > `to`
) AS tmp
ORDER BY one
       , two