Order by not working with group by clause - php

Question

I am using corequery of mysql in cakephp. I want the records in descending order. This is my table structure
enter code here
$coreQueryUser = $this->Message->query(
"select * from messages where messages.list_id = 3
group By (if(sender_id > reciever_id, sender_id, reciever_id)),
(if(sender_id > reciever_id, reciever_id, sender_id))
order by id desc
"
);
I want last message that belongs to (sender_id and reciver_id and viceversa) that belongs to list id 3
when i run this query i get the following output
<pre>Array
(
[0] => Array
(
[messages] => Array
(
[id] => 1
[sender_id] => 21
[reciever_id] => 10
[list_id] => 3
[message] => hello
[add_date] => 2016-09-25 00:00:00
[is_check] => 0
)
)
[1] => Array
(
[messages] => Array
(
[id] => 3
[sender_id] => 22
[reciever_id] => 10
[list_id] => 3
[message] => hello s
[add_date] => 2016-09-25 16:39:41
[is_check] => 0
)
)
)
but i wnat result like that:
Array
(
[0] => Array
(
[messages] => Array
(
[id] => 2
[sender_id] => 10
[reciever_id] => 21
[list_id] => 3
[message] => hello sir
[add_date] => 2016-09-25 00:00:00
[is_check] => 0
)
)
[1] => Array
(
[messages] => Array
(
[id] => 6
[sender_id] => 22
[reciever_id] => 10
[list_id] => 3
[message] => new
[add_date] => 2016-09-25 16:39:41
[is_check] => 0
)
)
)
Can anyone help me :(

Answer 1

The problem is that your query is against the sql standard because you have several fields in the select list that are neither in the group by list, nor are subject of an aggregate function, such as sum(). MySQL unfortunately allows such invalid queries to run under certain sql mode settings (the default settings of the most recent versions of MySQL would prevent such queries from running).
As MySQL documentation on group by clause says (bolding is mine):
If ONLY_FULL_GROUP_BY is disabled, a MySQL extension to the standard
SQL use of GROUP BY permits the select list, HAVING condition, or
ORDER BY list to refer to nonaggregated columns even if the columns
are not functionally dependent on GROUP BY columns. This causes MySQL
to accept the preceding query. In this case, the server is free to
choose any value from each group, so unless they are the same, the
values chosen are indeterminate, which is probably not what you want.
Furthermore, the selection of values from each group cannot be
influenced by adding an ORDER BY clause. Result set sorting occurs
after values have been chosen, and ORDER BY does not affect which
value within each group the server chooses.
You apparently want the latest record (with max(id) for each group. The proper way is to have a subquery that returns the max(id) per group and in the outer query join back to your main table using the ids to get the value of the other fields:
select m.*
from
messages m
inner join (
select max(id) as maxid
from messages
where messages.list_id = 3
group By (if(sender_id > reciever_id, sender_id, reciever_id)),
(if(sender_id > reciever_id, reciever_id, sender_id))
) t1 on m.id=t1.maxid

Answer 2

This code working:
SELECT * FROM generate_invoice
WHERE id IN
(
SELECT max(id) as id
FROM generate_invoice
GROUP by pay_id
ORDER by id DESC
)

Answer 3

How to group by DESC order
Try
SELECT * FROM ( SELECT * FROM generate_invoice ORDER BY id DESC ) AS g GROUP BY g.pay_id
OR
Use this code
SELECT m1.*,m2.* FROM generate_invoice m1 LEFT JOIN generate_invoice m2 ON (m1.pay_id = m2.pay_id AND m1.id < m2.id ) order by m1.id desc