query optimisation with join on ordered data - optimization

Question

My question concerns the optimization of a query sql.
My query retrieves a list of members and their last training.
To get the latest training I do a join on the result of a query returning a complete list of training for all members.
This query works but it is very slow, I'm really interrested if someone would have a solution for it to execute faster.
My query (about 16s):
SELECT
m.nom,
m.prenom,
m.ville,
m.maj,
mbf.libelle,
mbf.datefin,
m.id as idmb
FROM
membres m
LEFT JOIN (
select *
from membreform
where idformation = 1
order by datefin DESC
) as mbf ON mbf.idmembre = m.id
WHERE
role > 0 AND visible = 1
group by m.id
ORDER BY m.maj DESC
limit 0 , 20
My data structure :
membreform (1000 entries)
id int(11) NOT NULL AUTO_INCREMENT,
idmembre int(11) NOT NULL,
libelle varchar(128) NOT NULL,
idformation int(11) NOT NULL,
datedebut date NOT NULL,
datefin date NOT NULL DEFAULT '0000-00-00',
descript text NOT NULL,
KEY id (id),
KEY idmembre (idmembre),
KEY idformation (idformation)
membres (500 entries)
id int(3) NOT NULL AUTO_INCREMENT,
nom varchar(255) NOT NULL,
prenom varchar(255) NOT NULL,
ville varchar(255) NOT NULL,
email varchar(255) NOT NULL,
maj datetime NOT NULL,
role tinyint(4) NOT NULL DEFAULT '1',
PRIMARY KEY (id),
KEY role (role),
KEY maj (maj)
I tested this other way (about 0.40s) but I dont find that really clean
SELECT
m.nom,
m.prenom,
m.ville,
m.maj,
m.id as idmb,
(select
libelle
from
membreform
where
idformation = 1
AND m.id = membreform.idmembre
order by datefin DESC
limit 1
) libelle,
(select
datefin
from
membreform
where
idformation = 1
AND m.id = membreform.idmembre
order by datefin DESC
limit 1
) datefin
FROM
membres m
WHERE
role > 0 AND visible = 1
group by m.id
ORDER BY m.maj DESC
limit 0 , 20
I'm open to any suggestions because I am a bit stuck
thank you

Answer 1

You can use temporary table to increase performace. E.g (MS SQL)
1 Step - Get the memberform data into temp table by adding all relevant where conditions
select *
INTO #TempMembreform
from membreform
where idformation = 1 ...
order by datefin DESC
2 step - do the left outer join as you did in the above first example.
E.g.
SELECT
m.nom,
m.prenom,
m.ville,
m.maj,
mbf.libelle,
mbf.datefin,
m.id as idmb
FROM
membres m
LEFT JOIN #TempMembreForm as mbf
ON mbf.idmembre = m.id
WHERE
role > 0 AND visible = 1
group by m.id
ORDER BY m.maj DESC
limit 0 , 20
3 Step - add NOLOCK keyword if the data is not mision crical (e.g. Bank tracnsactions )
select *
INTO #TempMembreform
from membreform WITH(NOLOCK)
where idformation = 1
order by datefin DESC
SELECT
m.nom,
m.prenom,
m.ville,
m.maj,
mbf.libelle,
mbf.datefin,
m.id as idmb
FROM
membres m with(nolock)
LEFT JOIN #TempMembreForm as mbf
ON mbf.idmembre = m.id
WHERE
role > 0 AND visible = 1
group by m.id
ORDER BY m.maj DESC
limit 0 , 20
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