How to speed up this SQL Query?

Question

I am trying to fetch data from a SQL DB via PHPmyAdmin but it takes ages to excute my query. Do you have any idea how to speed up my query ?

My DB has the following structure

Table joueurs

| id_joueur | mail |

Table paires

| paires.annee | idj1 | idj2 |

Thanks alot

/* mail from all players being first memeber of a pair (idj1) 
in 2015, 2016 and 2017 and removing doubles*/

SELECT 
    mail
from 
    joueurs 
where 
    (joueurs.id_joueur in
        (SELECT idj1
        FROM paires
        WHERE  (paires.annee = 2015 OR paires.annee = 2016 OR paires.annee = 2017)
        )
    )
GROUP BY mail
HAVING COUNT(*) > 0

Answer 1

I would remove the subquery and just join the two tables. And also where clause might be better with a condition like paires.annee > 2014 and paires.annee < 2018 . But the only way to improve it is to add indices to the tables.

SELECT 
    j.mail
FROM
    joueurs j 
JOIN paires p on p.idj1 = j.id_joueur
WHERE p.annee > 2014 and p.annee < 2018  
GROUP BY j.mail
HAVING COUNT(*) > 0

Answer 2

You can use Exists on place of in, something like this

SELECT 
    j.mail
from 
    joueurs j
where 
   Exists
        (SELECT idj1
        FROM paires
        WHERE  idj1 =j.id_joueur and (paires.annee = 2015 OR paires.annee = 2016 OR paires.annee = 2017  )
        )    
GROUP BY j.mail
HAVING COUNT(*) > 0

EDIT : SQL Server IN vs. EXISTS Performance here you can read about Exists and IN

Answer 3

My initial recommendation is:

select distinct j.mail
from joueurs j
where exists (select 1
              from paires p
              where p.idj1 = j.id_joueur and p.annee in (2015, 2016, 2017)
             );

The having clause does nothing. For performance, you want an index on paires(idj1, annee) .

If this still takes a long time, what happens if you remove the distinct ? Are the results still acceptable?