I have several tables I need help to generate a query string. I am currently querying each of the tables and combining the results in the frontend which is making too many requests to the backend
Below is the structure of my tables (See this Sample sqlfiddle )
I guess each
id column in each of your tables is unique, that is each table has no repeated
id values. That's definitely the case in your fiddle.
And, I guess no user makes repeated attempts to answer a particular question in a particular event.
Here's a pure SQL query to get what you want. (https://www.db-fiddle.com/f/kRKsYAg954msn7bebtgUpg/2)
SELECT question_attempts.event_id, users.id user_id, users.first_name, users.last_name, SUM(questions.points) points FROM question_attempts JOIN questions ON question_attempts.question_id = questions.id JOIN answers ON question_attempts.answer_id = answers.id JOIN users ON question_attempts.user_id = users.id WHERE answers.is_correct = 1 GROUP BY question_attempts.event_id, users.id, users.first_name, users.last_name
Why does this work? Your
question_attempts table ties all the other tables together.
JOIN questions ON question_attempts.question_id = questions.idpulls in the question for each answer attempt. We need that because it says how many
pointsthe question is worth.
JOIN answers ON question_attempts.answer_id = answers.idpulls in the answer for each attempt. We need that because we need to know whether the particular answer
JOIN users ON question_attempts.user_id = users.idgets us the users' names.
Then, the SUM / GROUP BY adds up the points for correct answer for each event and user.
This query gets back all your events and users. You can add
WHERE ... AND question_attempts.event_id = 6
or some such thing to get the results for just one event.
And you can use
ORDER BY question_attempts.event_id, SUM(questions.points) DESC, users.id
to get your output in descending order of score (highest first) for each event.
This is example where triggers would come in handy. Use them to calculate Points directly into a table column. One you will have milions of rows and each time you gonna calculate this... over time it will get worst and worst.
Everytime you update answers you will update user row to update points.
Because your problem seems to be in houw to use ranking, I created an example on your questions table, and added a RANK on the points:
It is an example how to do RANKing (actually DENSE_RANK) in MySQL 5.6. When you are using MySQL 8.0 then you should user RANK or DENSE_RANK
SET @R:=0; SET @P:=0; SELECT id, description, points, CASE WHEN @P=points THEN @R ELSE @R:[email protected]+1 END as `RANK`, @P:=points FROM questions ORDER BY points DESC
For output, see fiddle, or:
|5||What was the first disease to be discovered||3.5||1||3.5|
|10||A child has more bones than an adult||3||2||3|
|8||Average time to complete a Marathon is 2hrs||3||2||3|
|7||An earthworm can grow back when cut||2||3||2|
|6||The statement a swarm of butterfly is valid||2||3||2|
|4||Sudan is the largest country in Africa||2||3||2|
|3||A cat dies 9 times||2||3||2|
|2||Blood color changes||2||3||2|
|1||Water is blue||2||3||2|
|9||What is the value of one plus one divide two?||1||4||1|
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