MySQL join on substring is slow - mysql

Question

I have a query where I do a join on a substring, the problem is that this is really slow to complete. Is there a more effecient way to write this?
SELECT *, SUM(s.pris*s.antall) AS total, SUM(s.antall) AS antall
FROM ecs_statistikk AS s
JOIN butikk_ordre AS bo ON ordreId=bo.ecs_ordre_id AND butikkNr=bo.site_id
JOIN ecs_supplier AS l ON SUBSTRING( s.artikkelId, 1,2 )=l.lev_id
WHERE s.salgsDato>='2016-6-01' AND s.salgsDato<='2016-09-30'
GROUP BY l.lev_id ORDER BY total DESC

Answer 1

First, I would check indexes. For this query:
SELECT *, SUM(s.pris*s.antall) AS total, SUM(s.antall) AS antall
FROM ecs_statistikk s JOIN
butikk_ordre bo
ON s.ordreId = bo.ecs_ordre_id AND
s.butikkNr = bo.site_id JOIN
ecs_supplier l
ON SUBSTRING(s.artikkelId, 1, 2 ) = l.lev_id
WHERE s.salgsDato >= '2016-06-01' AND s.salgsDato <= '2016-09-30'
GROUP BY l.lev_id
ORDER BY total DESC ;
You want indexes on ecs_statistikk(salgsDato, ordreId, butikkNr, artikkelId), butikk_ordre(ecs_ordre_id, site_id), and ecs_supplier(lev_id)`.
Next, I would question whether you need the last JOIN at all. Does this do what you want?
SELECT LEFT(s.artikkelId, 2) as lev_id, *,
SUM(s.pris*s.antall) AS total, SUM(s.antall) AS antall
FROM ecs_statistikk s JOIN
butikk_ordre bo
ON s.ordreId = bo.ecs_ordre_id AND
s.butikkNr = bo.site_id
WHERE s.salgsDato >= '2016-06-01' AND s.salgsDato <= '2016-09-30'
GROUP BY LEFT(s.artikkelId, 2)
ORDER BY total DESC ;