Pushing pointers to followers with the metadata (MySQL Query) - php

Question

I’ve seen the following question on StackOverflow, Intelligent MySQL GROUP BY for Activity Streams posted by Christian Owens 12/12/12.
So I decided to try out the same approach, make two tables similar to those of his. And then I pretty much copied his query which I do understand.
This is what I get out from my sandbox:
Array
(
[0] => Array
(
[id] => 0
[user_id] => 1
[action] => published_post
[object_id] => 776286559146635
[object_type] => post
[stream_date] => 2015-11-24 12:28:09
[rows_in_group] => 1
[in_collection] => 0
)
)
I am curious, since looking at the results in Owens question, I am not able to fully get something, and does he perform additional queries to grab the actual metadata? And if yes, does this mean that one can do it from that single query or does one need to run different optimized sub-queries and then loop through the arrays of data to render the stream itself.
Thanks a lot in advanced.
Array
(
[0] => Array
(
[id] => 0
[user_id] => 1
[fullname] => David Anderson
[action] => hearted
[object_id] => array (
[id] => 3438983
[title] => Grand Theft Auto
[Category] => Games
)
[object_type] => product
[stream_date] => 2015-11-24 12:28:09
[rows_in_group] => 1
[in_collection] => 1
)
)

Answer 1

In "pseudo" code you need something like this
$result = $pdo->query('
SELECT stream.*,
object.*,
COUNT(stream.id) AS rows_in_group,
GROUP_CONCAT(stream.id) AS in_collection
FROM stream
INNER JOIN follows ON stream.user_id = follows.following_user
LEFT JOIN object ON stream.object_id = object.id
WHERE follows.user_id = '0'
GROUP BY stream.user_id,
stream.verb,
stream.object_id,
stream.type,
date(stream.stream_date)
ORDER BY stream.stream_date DESC
');
then parse the result and convert it in php
$data = array(); // this will store the end result
while($row = $result->fetch(PDO::FETCH_ASSOC)) {
// here for each row you get the keys and put it in a sub-array
// first copy the selected `object` data into a sub array
$row['object_data']['id'] = $row['object.id'];
$row['object_data']['title'] = $row['object.title'];
// remove the flat selected keys
unset($row['object.id']);
unset($row['object.title']);
...
$data[] = $row; // move to the desired array
}
you should get
Array
(
[0] => Array
(
[id] => 0
[user_id] => 1
[fullname] => David Anderson
[verb] => hearted
[object_data] => array (
[id] => 3438983
[title] => Grand Theft Auto
[Category] => Games
)
[type] => product
[stream_date] => 2015-11-24 12:28:09
[rows_in_group] => 1
[in_collection] => 1
)
)

Answer 2

It seems that you want a query where you can return the data you're actually able to get plus the user fullname and the data related to the object_id.
I think that the best effort would be to include some subqueries in your query to extract these data:
Fullname: something like (SELECT fullname FROM users WHERE id = stream.user_id) AS fullname... or some modified version using the stream.user_id, as we can't identify in your schema where this fullname comes from;
Object Data: something like (SELECT CONCAT_WS(';', id, title, category_name) FROM objects WHERE id = stream.object_id) AS object_data. Just as the fullname, we can't identify in your schema where these object data comes from, but I'm assuming it's an objects table.
One object may have just one title and may have just one category. In this case, the Object Data subquery works great. I don't think an object can have more than one title, but it's possible to have more than one category. In this case, you should GROUP_CONCAT the category names and take one of the two paths:
Replace the category_name in the CONCAT_WS for the GROUP_CONCAT of all categories names;
Select a new column categories (just a name suggestion) with the subquery which GROUP_CONCAT all categories names;
If your tables were like te first two points of my answer, a query like this may select the data, just needing a proper parse (split) in PHP:
SELECT
MAX(stream.id) as id,
stream.user_id,
(select fullname from users where id = stream.user_id) as fullname,
stream.verb,
stream.object_id,
(select concat_ws(';', id, title, category_name) from objects where id = stream.object_id) as object_data,
stream.type,
date(stream.stream_date) as stream_date,
COUNT(stream.id) AS rows_in_group,
GROUP_CONCAT(stream.id) AS in_collection
FROM stream
INNER JOIN follows ON 1=1
AND stream.user_id = follows.following_user
WHERE 1=1
AND follows.user_id = '0'
GROUP BY
stream.user_id,
stream.verb,
stream.object_id,
stream.type,
date(stream.stream_date)
ORDER BY stream.stream_date DESC;
In ANSI SQL you can't reference columns not listed in your GROUP BY, unless they're in aggregate functions. So, I included the id as an aggregation.