Question

I need to order my query by date first…

So I used this:

SELECT * FROM `mfw_navnode` order by `id` DESC

I wanted to order my results from last to first.

Then what I am trying to do

is to add a query over it, which would group my results by node_name..

The result should be..all the top nodes grouped by “category/node name type”, while the first node that I see is was ordered the highest for its category in the first query..

I thought to do something like this:

SELECT * FROM( 
SELECT * FROM `mfw_navnode` order by `id` DESC) AS DD
WHERE (node_name='Eby' OR node_name='Laa'  OR node_name='MIF' OR node_name='Amaur' OR node_name='Asn' )
GROUP BY DD.node_name

I get no result..or any response from phpmyadmin when I input that result..

Where do I get wrong?

Note , I dont want to group my results and then order them..

I want them to be ordered, and then grouped. After being grouped..I want the result of each group to have the highest value ..from the other rows in the group

Answer 1

It is not sufficient to perform the ordering first, as even then MySQL makes no guarantee over which record it will select for each group. From the manual:

The server is free to choose any value from each group, so unless they are the same, the values chosen are indeterminate.

You must instead identify the records of interest with a subquery, then join the result with your table again in order to obtain the related values:

SELECT *
FROM   mfw_navnode NATURAL JOIN (
         SELECT node_name, MAX(id) AS id FROM mfw_navnode GROUP BY node_name
       ) AS DD
WHERE  node_name IN ('Eby', 'Laa', 'MIF', 'Amaur', 'Asn')