Question

I’m designing a project for quizzes and quizz results. So I have two tables: quizz_result and quizz. quizz has primary key on ID and quizz_result has foreign key QUIZZ_ID to quizz identity.

Query below is designed to take public quizzes ordered by date with asociated informations: if current user (683735) took this quizz and has a valid result (>0) and how many people filled this quizz till this point in time.

So i did this simple query with two left joins:

select     
  a.*,  
  COUNT(countt.QUIZZ_ID) SUMFILL
from 
  quizz a
  left join quizz_result countt
    on countt.QUIZZ_ID = a.ID 
group by 
   a.ID

And added indexes on these columns:
Quizz:

ID, (ID, DATE), PUBLIC, (PUBLIC, DATE)

And on quizz_result:

ID, (QUIZZ_ID, USER_ID), QUIZZ_ID, USER_ID, (QUIZZ_ID, QUIZZ_RESULT_ID)

But still when I do query it takes like about one minute. And i have only 34k rows in QUIZZ_RESULTS and 120 rows in QUIZZ table.

When I do EXPLAIN on this query I get this:

SELECT TYPE: simple, possible keys:  IDX_PUBLIC,DATE, rows: 34  extra: Using where; Using temporary; Using filesort
SELECT TYPE: simple, possible keys: IDX_QUIZZ_USER,IDX_QUIZZ_RES_RES_QUIZ,IDX_USERID,I..., rows: 1, extra: nothing here
SELECT TYPE: simple, possible keys: IDX_QUIZZ_USER,IDX_QUIZ_RES_RES_QUIZZ,ID_RESULT_ID, rows: 752, extra:  Using index

And I don’t know what to do to optimise this query. I see this:

Using where; Using temporary; Using filesort

But still I don’t know how to get this better, or maybe number of rows in last select is to hight? 752?

How can I optimise this query?

EDIT: I’ve upadated query to this one with only one left join because it has the same long execution time.

EDIT2: I did remove everything to and thats it: this simple select with one query takes 1s to execute. How to optimise it?

Answer 1

I’ve changed it to this:

select     
  a.*,  
  COUNT(a.ID) SUMFILL
from 
  quizz a
  left join quizz_result countt
    on countt.QUIZZ_ID = a.ID 
group by 
   a.ID

And it’s good now.