Question

I hope you will be able to help me, this has been giving me headaches 😀

First, a bit of context:

Using the following table and data:

+-------------+---------+-------------+
| host_name   | service | last_change |
+-------------+---------+-------------+
| test.com    | PING    |  1327004398 |
| test.com    | HTTP    |  1327004536 |
| test.com    | MYSQL   |  1327004392 |
| test2.com   | PING    |  1327127720 |
| test2.com   | HTTP    |  1327004391 |
| test3.com   | PING    |  1327213842 |
| test4.com   | PING    |  1327004368 |
+-------------+---------+-------------+

What I’d lke to do is to print this out to a table with the host_name cell that spans the right amount of rows, a bit like so:

 +-------------+---------+-------------+
 | host_name   | service | last_change |
 +-------------+---------+-------------+
 |             | PING    |  1327004398 |
 | test.com    | HTTP    |  1327004536 |
 |             | MYSQL   |  1327004392 |
 +-------------+---------+-------------+

I am already able to do this, using a query that looks like this:

SELECT
    host_name,
    group_concat(service SEPARATOR '|') as service,
    group_concat(last_change SEPARATOR '|') as last_change,    

FROM table

GROUP BY host_name

And then by doing some manipulations (exploding results where pipes are found).

The problem I have:

I’d like to do the same thing but sort the results based on last_change. I tried to do the following:

SELECT
    host_name,
    group_concat(service SEPARATOR '|') as service,
    group_concat(last_change SEPARATOR '|') as last_change,    

FROM
(
    SELECT * FROM table ORDER BY last_change DESC
) as tmp_table

GROUP BY host_name

But it doesn’t seem to work. Changing the DESC to ASC doesn’t even change the results I get.

If I run the subquery that orders the results by itself, I get the expected results except the results arent grouped by host_name (obviously since it lacks the group_concat and group by statements).

Any ideas ?

I appreciate it A LOT.

Answer 1

I didn’t get exactly what you’re trying to do here. Do you want results inside the group ordered, or the whole resultset?
Try this for the first case:

SELECT
    host_name,
    group_concat(service ORDER BY last_change DESC SEPARATOR '|') as service,
    group_concat(last_change ORDER BY last_change DESC SEPARATOR '|') as last_change
FROM table
GROUP BY host_name

And this for second:

SELECT
    host_name,
    group_concat(service SEPARATOR '|') as service,
    group_concat(last_change SEPARATOR '|') as last_change
FROM table
GROUP BY host_name
ORDER BY table.last_change