Mysql Subquery Work Slowly - mysql

Question

I use view has subquery and concat in mysql. Normally, query works rapidly, but if query has subquery works very slowly.
This code is running quickly (approximate 1 seconds)
CREATE OR REPLACE VIEW ilceler AS (
SELECT I.id, I.modulid, I.id as icerikidsi,
MAX(IF(D.alanid=2,D.textkisa,NULL)) AS ilceadi,
MAX(IF(D.alanid=2,D.id,NULL)) AS ilceadi_i,
I.seo_description,
I.seo_h1,
I.seo_h2,
I.seo_h3,
I.seo_h4,
I.seo_imgalt,
I.seo_imgtitle,
I.seo_keywords,
I.seo_pagetitle,
I.seo_url,
I.seo_urltitle
FROM datalar as D LEFT JOIN icerikler as I ON D.icerikid=I.id WHERE D.modulid='3' GROUP BY D.icerikid ORDER BY sehiradi asc )
But this code is working very very slowly (approximate 20 seconds)
CREATE OR REPLACE VIEW ilceler AS (
SELECT I.id, I.modulid, I.id as icerikidsi,
MAX(IF(D.alanid=2,D.textkisa,NULL)) AS ilceadi,
MAX(IF(D.alanid=2,D.id,NULL)) AS ilceadi_i,
( SELECT CONVERT ( GROUP_CONCAT(D2.id SEPARATOR ' ₋ ' ) USING UTF8 )FROM datalar as D1
LEFT JOIN datalar as D2 ON D1.iliskialanid=D2.id WHERE D1.modulid='3' AND D1.alanid='3' AND D1.icerikid=icerikidsi ) as sehiradi_a ,
( SELECT GROUP_CONCAT(iliskiid SEPARATOR ' ₋ ') FROM datalar WHERE alanid='3' AND modulid='3' AND icerikid=icerikidsi ) as sehiradi_i,
( SELECT GROUP_CONCAT(D2.textkisa SEPARATOR ' ₋ ' ) FROM datalar as D1 LEFT JOIN datalar as D2 ON D1.iliskialanid=D2.id
WHERE D1.modulid='3' AND D1.alanid='3' AND D1.icerikid=icerikidsi ) as sehiradi ,
I.seo_description,
I.seo_h1,
I.seo_h2,
I.seo_h3,
I.seo_h4,
I.seo_imgalt,
I.seo_imgtitle,
I.seo_keywords,
I.seo_pagetitle,
I.seo_url,
I.seo_urltitle
FROM datalar as D LEFT JOIN icerikler as I ON D.icerikid=I.id WHERE D.modulid='3' GROUP BY D.icerikid ORDER BY sehiradi asc )
Why? Where do I make mistake?
I am waiting for your help.

Answer 1

Your sub queries rely on the values of the select, hence each of those 3 sub queries needs to be performed for each returned row. With a small number of rows this isn't an issue but with lots of rows this can rapidly add up.
Normal solution is to join against the sub query (hence it is done once for all rows and you just join the results).
For example:-
SELECT I.id,
I.modulid,
I.id as icerikidsi,
MAX(IF(D.alanid=2,D.textkisa,NULL)) AS ilceadi,
MAX(IF(D.alanid=2,D.id,NULL)) AS ilceadi_i,
sub1.sehiradi_a ,
sub2.sehiradi_i,
sub1.sehiradi ,
I.seo_description,
I.seo_h1,
I.seo_h2,
I.seo_h3,
I.seo_h4,
I.seo_imgalt,
I.seo_imgtitle,
I.seo_keywords,
I.seo_pagetitle,
I.seo_url,
I.seo_urltitle
FROM datalar as D
LEFT JOIN icerikler as I ON D.icerikid=I.id
LEFT OUTER JOIN
(
SELECT D1.icerikid, CONVERT ( GROUP_CONCAT(D2.id SEPARATOR ' ₋ ' ) USING UTF8 ) AS sehiradi_a, GROUP_CONCAT(D2.textkisa SEPARATOR ' ₋ ' ) AS sehiradi
FROM datalar as D1
LEFT JOIN datalar as D2 ON D1.iliskialanid=D2.id
WHERE D1.modulid='3'
AND D1.alanid='3'
GROUP BY D1.icerikid
) sub1
ON sub1.icerikid = I.id
LEFT OUTER JOIN
(
SELECT icerikid, GROUP_CONCAT(iliskiid SEPARATOR ' ₋ ') AS sehiradi_i
FROM datalar
WHERE alanid='3'
AND modulid='3'
GROUP BY icerikid
) sub2
ON sub2.icerikid = I.id
WHERE D.modulid='3'
GROUP BY D.icerikid
ORDER BY sehiradi asc
Or depending on your actual database design you might be able to simplify it to
SELECT I.id,
I.modulid,
I.id as icerikidsi,
MAX(IF(D.alanid=2,D.textkisa,NULL)) AS ilceadi,
MAX(IF(D.alanid=2,D.id,NULL)) AS ilceadi_i,
sub1.sehiradi_a ,
sub1.sehiradi_i,
sub1.sehiradi ,
I.seo_description,
I.seo_h1,
I.seo_h2,
I.seo_h3,
I.seo_h4,
I.seo_imgalt,
I.seo_imgtitle,
I.seo_keywords,
I.seo_pagetitle,
I.seo_url,
I.seo_urltitle
FROM datalar as D
LEFT JOIN icerikler as I ON D.icerikid=I.id
LEFT OUTER JOIN
(
SELECT D1.icerikid,
CONVERT ( GROUP_CONCAT(D2.id SEPARATOR ' ₋ ' ) USING UTF8 ) AS sehiradi_a,
GROUP_CONCAT(D2.textkisa SEPARATOR ' ₋ ' ) AS sehiradi,
GROUP_CONCAT(DISTINCT D1.iliskiid SEPARATOR ' ₋ ') AS sehiradi_i
FROM datalar as D1
LEFT JOIN datalar as D2 ON D1.iliskialanid=D2.id
WHERE D1.modulid='3'
AND D1.alanid='3'
GROUP BY D1.icerikid
) sub1
ON sub1.icerikid = I.id
WHERE D.modulid='3'
GROUP BY D.icerikid
ORDER BY sehiradi asc
However there is a minor issue here. In MySQL a view cannot contain a FROM that takes data from a sub query. As such to use this syntax in your view you would need to split the sub queries off into their own views. Then you could join against the view rather than the sub query.