Help on how to join these two queries MySql

First, I think the and qs.slot=qa.slot part should be moved into the corresponding JOIN .

I'll kick the columns itemtype , itemmodule , finalgrade and aggregationstatus into tables gg and gi . If I missed those kicks, let me know.

This is the table graph you have:

         qc --- q
                |
quiz --- qs --- qa --- qas --- u --- gg --- gi

In this graph, qc is in the first query PORTUGUES and in the second query MATEMATICA . Each result, before being applied GROUP BY , brings exactly one tuple of each of these tables.

What happens is that you will need to bring two tuples from some tables to join, one from Portuguese and one from math (before GROUP BY ). This way, you will have a graph like this:

          pqc --- pq
                  |
pquiz --- pqs --- pqa --- pqas
                          |
                          u --- gg --- gi
                          |
mquiz --- mqs --- mqa --- mqas
                  |
          mqc --- mq

Where the tables starting with p are from questions in Portuguese and starting with m are from math questions. Again, a tuple of each table in the above graph is chosen before the GROUP BY is done. There are cases where the same physical table appears in two different places in the graph as if they were two different tables.

The query looks like this:

-- Campos a selecionar.
SELECT
    AVG(IFNULL(pqas.fraction, 0)) * 10 AS MediaPT,
    AVG(IFNULL(mqas.fraction, 0)) * 10 AS MediaMT,
    gg.finalgrade AS NotaGeral,
    u.firstname AS Aluno,
    u.username AS Usuario,
    u.lastname AS siem,
--  u.id, -- removido
    u.department AS Turma,
    u.institution AS Escola,
    pqc.name AS catp,
    mqc.name AS catm

-- Tabelas que independem da disciplina.
FROM mdl_user u
INNER JOIN mdl_grade_grades gg ON gg.userid = u.id
INNER JOIN mdl_grade_items gi ON gi.'id' = gg.'itemid'

-- Tabelas para relacionar as tuplas de português.
INNER JOIN mdl_question_attempt_steps pqas ON u.id = pqas.userid
INNER JOIN mdl_question_attempts pqa ON pqa.id = pqas.questionattemptid
INNER JOIN mdl_question pq ON pq.id = pqa.questionid
INNER JOIN mdl_quiz_slots pqs ON pqs.questionid = pqa.questionid AND pqs.slot = pqa.slot
INNER JOIN mdl_quiz pquiz ON pquiz.id = pqs.quizid
INNER JOIN mdl_question_categories pqc ON pqc.id = pq.category

-- Tabelas para relacionar as tuplas de matemática.
INNER JOIN mdl_question_attempt_steps mqas ON u.id = mqas.userid
INNER JOIN mdl_question_attempts mqa ON mqa.id = mqas.questionattemptid
INNER JOIN mdl_question mq ON mq.id = mqa.questionid
INNER JOIN mdl_quiz_slots mqs ON mqs.questionid = mqa.questionid AND mqs.slot = mqa.slot
INNER JOIN mdl_quiz mquiz ON mquiz.id = mqs.quizid
INNER JOIN mdl_question_categories mqc ON mqc.id = mq.category

-- Parte do WHERE que não depende de disciplina.
WHERE substring(u.department, 2, 1) = 4
AND substr(gi.itemname, 1) = 4
AND substr(gi.itemname, -1) = 1
AND itemtype = "mod"
AND itemmodule = "quiz"
AND gg.finalgrade != "NULL"
AND aggregationstatus = "used"
AND u.lastname = 213

-- Parte do WHERE para filtrar apenas português nas tabelas p.
AND SUBSTR(pquiz.ano, 1, 4) = 2018
AND SUBSTR(pquiz.name, 1) = 4
AND SUBSTR(pquiz.name, -1) = 1
AND pqas.state != "todo"
AND pqas.state != "complete"
AND SUBSTR(pqc.name, 8) = "PORTUGUES"

-- Parte do WHERE para filtrar apenas matemática nas tabelas m.
AND SUBSTR(mquiz.ano, 1, 4) = 2018
AND SUBSTR(mquiz.name, 1) = 4
AND SUBSTR(mquiz.name, -1) = 1
AND mqas.state != "todo"
AND mqas.state != "complete"
AND SUBSTR(mqc.name, 8) = "MATEMATICA"

-- Final da query.
GROUP BY turma, u.id
ORDER BY turma ASC, 'Aluno' ASC

This approach is not very scalable in case you want results with 30 different subjects. In that case, I suggest you show how the modeling of the tables involved for a more in-depth answer is possible. Also, some things you put in the WHERE clauses (especially SUBSTR ) strongly suggest that your database needs some sort of restructuring if that is possible.