MySQL duplicate column on select from select - mysql

Question

I have a few tables:
resources (which contains all the posts)
pid | usrnm | title | link | content | stitle | sdesc | at | likes
tags (which contains all the tags and an ID)
id | slug
retags (which connects the resource and it's tags)
pid | tid
I'm trying to make a search engine with which you can search by multiple tags, a search value and order the results by newest or most liked.
The SQL I use for searching by tags is:
SELECT
resources.pid, resources.title
FROM resources
INNER JOIN retags ON resources.pid = retags.pid
INNER JOIN tags ON retags.tid = tags.id
GROUP BY resources.pid
HAVING
SUM(tags.slug = 'tag-z')
AND
SUM(tags.slug = 'tag-y')
How can I apply the SQL for the search value WHERE title LIKE '%bla%' and order ORDER BY at DESC to this tag search SQL?
I tried select from select but kept gettings errors like "Duplicate column pid", "Column 'pid' in field list is ambiguous" etc
Can someone help me with this SQL? Thanks
I've tried everything in StackOverflow like using an alias for column name on oneSELECT pid as pid_ ... and even on both selects but I still kept getting the same duplicate column error.
EDIT: The SQL I've been getting errors from:
SELECT * FROM
(SELECT * FROM resources
INNER JOIN retags ON resources.pid = retags.pid
INNER JOIN tags ON retags.tid = tags.id
GROUP BY resources.pid
HAVING
SUM(tags.slug = 'A2') AND
SUM(tags.slug = 'AS')
) AS tsr WHERE tsr.title LIKE '%bla%' ORDER BY tsr.`at` DESC
This is just one of them, I've tried a lot of different types from other posts and different errors I get from them.

Answer 1

The WHERE clause goes before the GROUP BY:
SELECT rs.pid, rs.title
FROM resources rs JOIN
retags rt
ON rs.pid = rt.pid JOIN
tags t
ON rt.tid = t.id
WHERE rs.title LIKE '%bla%'
GROUP BY rs.pid
HAVING SUM(t.slug = 'tag-z') AND
SUM(t.slug = 'tag-y')
ORDER BY MAX(rs.at);
Strictly speaking, the MAX() is not needed in the ORDER BY assuming that pid uniquely identifies each row in resources.
My guess is that at is in multiple rows, so you need to qualify the reference with the table it comes from. Note that I introduced table aliases so the query is easier to write and to read.