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SELECT 
  SQL_CALC_FOUND_ROWS products.product_id, 
  IF(
    shared_descr.product_id IS NOT NULL, 
    shared_descr.product, descr1.product
  ) as product, 
  IF(
    shared_descr.product_id IS NOT NULL, 
    shared_descr.youtube_link, products.youtube_link
  ) AS youtube_link, 
  cscart_aval_statuses_descr.descr as aval_descr 
FROM 
  cscart_products as products 
  LEFT JOIN cscart_product_descriptions as descr1 ON descr1.product_id = products.product_id 
  AND descr1.lang_code = 'se' 
  LEFT JOIN cscart_product_prices as prices ON prices.product_id = products.product_id 
  AND prices.lower_limit = 1 
  INNER JOIN cscart_products_categories as products_categories ON products_categories.product_id = products.product_id 
  INNER JOIN cscart_categories ON cscart_categories.category_id = products_categories.category_id 
  AND (
    cscart_categories.usergroup_ids = '' 
    OR FIND_IN_SET(
      0, cscart_categories.usergroup_ids
    ) 
    OR FIND_IN_SET(
      1, cscart_categories.usergroup_ids
    )
  ) 
  AND cscart_categories.status IN ('A', 'H') 
  LEFT JOIN cscart_ult_product_descriptions shared_descr ON shared_descr.product_id = products.product_id 
  AND shared_descr.company_id = 2 
  AND shared_descr.lang_code = 'se' 
  LEFT JOIN cscart_aval_statuses ON cscart_aval_statuses.aval_status_id = products.aval_status 
  LEFT JOIN cscart_aval_statuses_descr ON cscart_aval_statuses.aval_status_id = cscart_aval_statuses_descr.aval_status_id 
  AND cscart_aval_statuses.status = 'A' 
  AND cscart_aval_statuses_descr.lang_code = 'se' 
  LEFT JOIN cscart_product_popularity as popularity ON popularity.product_id = products.product_id 
WHERE 
  1 
  AND cscart_categories.category_id IN (
    258, 273, 274, 370, 383, 913, 296, 873, 
    912, 914, 278, 275, 905, 276, 277, 906, 
    352
  ) 
  AND cscart_categories.company_id = 2 
  AND (
    products.usergroup_ids = '' 
    OR FIND_IN_SET(0, products.usergroup_ids) 
    OR FIND_IN_SET(1, products.usergroup_ids)
  ) 
  AND products.status IN ('A') 
  AND prices.usergroup_id IN (0, 0, 1) 
GROUP BY 
  products.product_id 
ORDER BY 
  popularity.total desc, 
  product_id ASC 
LIMIT 
  0, 12

Query time 0.03511

Explain
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	products	ref	PRIMARY,status,product_id_idx,status_idx	status	3	const	594	Using index condition; Using where; Using temporary; Using filesort
1	SIMPLE	prices	ref	usergroup,product_id,lower_limit,usergroup_id	usergroup	3	mahm3t_cs443.products.product_id	1	Using where; Using index
1	SIMPLE	shared_descr	eq_ref	PRIMARY,product_id,company_id	PRIMARY	13	mahm3t_cs443.products.product_id,const,const	1	Using where
1	SIMPLE	cscart_aval_statuses	eq_ref	PRIMARY	PRIMARY	4	mahm3t_cs443.products.aval_status	1
1	SIMPLE	cscart_aval_statuses_descr	ref	aval_status_id	aval_status_id	10	mahm3t_cs443.cscart_aval_statuses.aval_status_id,const	1	Using where
1	SIMPLE	popularity	eq_ref	PRIMARY,total	PRIMARY	3	mahm3t_cs443.products.product_id	1
1	SIMPLE	descr1	eq_ref	PRIMARY,product_id	PRIMARY	9	mahm3t_cs443.products.product_id,const	1	Using where
1	SIMPLE	products_categories	ref	PRIMARY,pt,product_id_idx,category_id_idx,product_category_idx,category_product_idx	product_category_idx	3	mahm3t_cs443.products.product_id	3	Using index
1	SIMPLE	cscart_categories	eq_ref	PRIMARY,c_status,p_category_id,idx_category_id	PRIMARY	3	mahm3t_cs443.products_categories.category_id	1	Using index condition; Using where

Result

product_id	product	aval_descr
437	Frigolit / Cellplast EPS Vägg THERMO PLUS (λ=0,031)
443	Extuderad polystyren XPS 300 / XPS 250
439	Stenull ROCKWOOL FRONTROCK SUPER ▪ isolering av fasad	<p style="color: #FFAB00;">Skickas ut inom: Fråga om leveranstid</p>
435	Frigolit / Cellplast EPS Vägg GOLD (λ=0,038)
1805	Frigolit / Cellplast EPS Vägg BASIC (λ = 0,044)
1806	Frigolit / Cellplast EPS Vägg STANDARD (λ = 0,042)
434	Frigolit / Cellplast EPS Vägg SILVER (λ = 0,040)
436	Frigolit / Cellplast EPS Vägg THERMO (λ = 0,032)
10161	Stenull ROCKWOOL FRONTROCK PLUS ▪ isolering av fasad	<p style="color: #FFAB00;">Skickas ut inom: Fråga om leveranstid</p>
504	ATLAS Uni-Grunt \| snabbtorkande primer \| för förbehandling av mineralytor	<p>Skickas ut inom ung.10-12 arbetsdagar efter mottagandet av din betalning</p>
9865	Frigolit / Cellplast EPS Vägg GALAXY (λ = 0,033)
438	Stenull ROCKWOOL FRONTROCK L ▪ isolering av fasad	<p>Skickas ut inom ung. 6-10 arbetsdagar efter mottagandet av din betalning</p>