SELECT 
  SQL_CALC_FOUND_ROWS products.product_id, 
  IF(
    shared_descr.product_id IS NOT NULL, 
    shared_descr.product, descr1.product
  ) as product, 
  popularity.total as popularity, 
  stoc_intern, 
  pret_achizitie, 
  pret_revanzator, 
  gestiune 
FROM 
  cscart_products as products 
  LEFT JOIN cscart_product_options_inventory as inventory ON inventory.product_id = products.product_id 
  LEFT JOIN cscart_product_descriptions as descr1 ON descr1.product_id = products.product_id 
  AND descr1.lang_code = 'ro' 
  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_product_popularity as popularity ON popularity.product_id = products.product_id 
  LEFT JOIN cscart_ult_product_descriptions shared_descr ON shared_descr.product_id = products.product_id 
  AND shared_descr.company_id = 1 
  AND shared_descr.lang_code = 'ro' 
WHERE 
  1 
  AND cscart_categories.company_id = 1 
  AND (
    CASE products.tracking WHEN 'O' THEN inventory.amount > 0 WHEN 'B' THEN products.amount > 0 ELSE 1 END
  ) 
  AND popularity.total >= 1 
  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, 20

Query time 0.58746

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "1403.60"
    },
    "ordering_operation": {
      "using_temporary_table": true,
      "using_filesort": true,
      "grouping_operation": {
        "using_filesort": false,
        "nested_loop": [
          {
            "table": {
              "table_name": "inventory",
              "access_type": "system",
              "possible_keys": [
                "pc"
              ],
              "rows_examined_per_scan": 0,
              "rows_produced_per_join": 1,
              "filtered": "0.00",
              "const_row_not_found": true,
              "cost_info": {
                "read_cost": "0.00",
                "eval_cost": "0.10",
                "prefix_cost": "0.00",
                "data_read_per_join": "880"
              },
              "used_columns": [
                "product_id",
                "amount"
              ]
            }
          },
          {
            "table": {
              "table_name": "products",
              "access_type": "ref",
              "possible_keys": [
                "PRIMARY",
                "status"
              ],
              "key": "status",
              "used_key_parts": [
                "status"
              ],
              "key_length": "3",
              "ref": [
                "const"
              ],
              "rows_examined_per_scan": 1420,
              "rows_produced_per_join": 1420,
              "filtered": "100.00",
              "cost_info": {
                "read_cost": "356.43",
                "eval_cost": "142.00",
                "prefix_cost": "498.43",
                "data_read_per_join": "6M"
              },
              "used_columns": [
                "product_id",
                "status",
                "amount",
                "usergroup_ids",
                "tracking",
                "stoc_intern",
                "pret_achizitie",
                "pret_revanzator",
                "gestiune"
              ],
              "attached_condition": "((0 <> (case `maniamall_cscart`.`products`.`tracking` when 'O' then <cache>((NULL > 0)) when 'B' then (`maniamall_cscart`.`products`.`amount` > 0) else 1 end)) and ((`maniamall_cscart`.`products`.`usergroup_ids` = '') or (0 <> find_in_set(0,`maniamall_cscart`.`products`.`usergroup_ids`)) or (0 <> find_in_set(1,`maniamall_cscart`.`products`.`usergroup_ids`))))"
            }
          },
          {
            "table": {
              "table_name": "prices",
              "access_type": "ref",
              "possible_keys": [
                "usergroup",
                "product_id",
                "lower_limit",
                "usergroup_id"
              ],
              "key": "lower_limit",
              "used_key_parts": [
                "lower_limit",
                "product_id"
              ],
              "key_length": "6",
              "ref": [
                "const",
                "maniamall_cscart.products.product_id"
              ],
              "rows_examined_per_scan": 1,
              "rows_produced_per_join": 710,
              "filtered": "50.00",
              "using_index": true,
              "cost_info": {
                "read_cost": "387.27",
                "eval_cost": "71.00",
                "prefix_cost": "1027.70",
                "data_read_per_join": "16K"
              },
              "used_columns": [
                "product_id",
                "lower_limit",
                "usergroup_id"
              ],
              "attached_condition": "(`maniamall_cscart`.`prices`.`usergroup_id` in (0,0,1))"
            }
          },
          {
            "table": {
              "table_name": "popularity",
              "access_type": "eq_ref",
              "possible_keys": [
                "PRIMARY",
                "total"
              ],
              "key": "PRIMARY",
              "used_key_parts": [
                "product_id"
              ],
              "key_length": "3",
              "ref": [
                "maniamall_cscart.products.product_id"
              ],
              "rows_examined_per_scan": 1,
              "rows_produced_per_join": 236,
              "filtered": "33.33",
              "cost_info": {
                "read_cost": "0.00",
                "eval_cost": "23.66",
                "prefix_cost": "1098.70",
                "data_read_per_join": "7K"
              },
              "used_columns": [
                "product_id",
                "total"
              ],
              "attached_condition": "(`maniamall_cscart`.`popularity`.`total` >= 1)"
            }
          },
          {
            "table": {
              "table_name": "shared_descr",
              "access_type": "eq_ref",
              "possible_keys": [
                "PRIMARY",
                "product_id",
                "company_id"
              ],
              "key": "PRIMARY",
              "used_key_parts": [
                "product_id",
                "lang_code",
                "company_id"
              ],
              "key_length": "13",
              "ref": [
                "maniamall_cscart.products.product_id",
                "const",
                "const"
              ],
              "rows_examined_per_scan": 1,
              "rows_produced_per_join": 236,
              "filtered": "100.00",
              "cost_info": {
                "read_cost": "0.00",
                "eval_cost": "23.66",
                "prefix_cost": "1122.37",
                "data_read_per_join": "902K"
              },
              "used_columns": [
                "product_id",
                "lang_code",
                "company_id",
                "product"
              ]
            }
          },
          {
            "table": {
              "table_name": "descr1",
              "access_type": "eq_ref",
              "possible_keys": [
                "PRIMARY",
                "product_id"
              ],
              "key": "PRIMARY",
              "used_key_parts": [
                "product_id",
                "lang_code"
              ],
              "key_length": "9",
              "ref": [
                "maniamall_cscart.products.product_id",
                "const"
              ],
              "rows_examined_per_scan": 1,
              "rows_produced_per_join": 236,
              "filtered": "100.00",
              "cost_info": {
                "read_cost": "0.00",
                "eval_cost": "23.66",
                "prefix_cost": "1146.03",
                "data_read_per_join": "904K"
              },
              "used_columns": [
                "product_id",
                "lang_code",
                "product"
              ]
            }
          },
          {
            "table": {
              "table_name": "products_categories",
              "access_type": "ref",
              "possible_keys": [
                "PRIMARY",
                "pt"
              ],
              "key": "pt",
              "used_key_parts": [
                "product_id"
              ],
              "key_length": "3",
              "ref": [
                "maniamall_cscart.products.product_id"
              ],
              "rows_examined_per_scan": 1,
              "rows_produced_per_join": 330,
              "filtered": "100.00",
              "using_index": true,
              "cost_info": {
                "read_cost": "191.42",
                "eval_cost": "33.07",
                "prefix_cost": "1370.53",
                "data_read_per_join": "5K"
              },
              "used_columns": [
                "product_id",
                "category_id"
              ]
            }
          },
          {
            "table": {
              "table_name": "cscart_categories",
              "access_type": "eq_ref",
              "possible_keys": [
                "PRIMARY",
                "c_status",
                "p_category_id"
              ],
              "key": "PRIMARY",
              "used_key_parts": [
                "category_id"
              ],
              "key_length": "3",
              "ref": [
                "maniamall_cscart.products_categories.category_id"
              ],
              "rows_examined_per_scan": 1,
              "rows_produced_per_join": 16,
              "filtered": "5.00",
              "cost_info": {
                "read_cost": "0.00",
                "eval_cost": "1.65",
                "prefix_cost": "1403.60",
                "data_read_per_join": "42K"
              },
              "used_columns": [
                "category_id",
                "company_id",
                "usergroup_ids",
                "status"
              ],
              "attached_condition": "((`maniamall_cscart`.`cscart_categories`.`company_id` = 1) and ((`maniamall_cscart`.`cscart_categories`.`usergroup_ids` = '') or (0 <> find_in_set(0,`maniamall_cscart`.`cscart_categories`.`usergroup_ids`)) or (0 <> find_in_set(1,`maniamall_cscart`.`cscart_categories`.`usergroup_ids`))) and (`maniamall_cscart`.`cscart_categories`.`status` in ('A','H')))"
            }
          }
        ]
      }
    }
  }
}

Result

product_id product popularity stoc_intern pret_achizitie pret_revanzator gestiune
1437277 Covoras rotund imitatie blana, pentru bradul de Craciun, diametru 122 cm, blanita culoare alb 107620 -99 0.00 86.00 Y
1903062 Covoras rotund imitatie blana, pentru bradul de Craciun, diametru 120 cm, prindere Velcro, culoare alb 59267 -99 86.28 76.92 Y
1128285 Set perne decorative pentru mobilier paleti, perna sezut 120x70 cm + perna spate 120x40 cm, culoare gri 51087 0 0.00 19.00 Y
480519 Kit pentru Reparatie Parbriz sau Geam Auto 47624 -99 17.10 44.00 Y
447578 Covoras suport protectie pentru piscina, dimensiuni 335x335cm 45719 -99 33.03 58.00 Y
522515 Proiector Laser LED Tip Shower 3D Metal Interior/Exterior, 24 Efecte de Lumini Miscatoare si Telecomanda 45320 -99 118.73 124.00 Y
241391 Masina de Tuns Caini, Pisici sau Diverse Animale, Include 4 Capete de Tuns 42478 -99 44.17 63.00 Y
1118346 Piscina pentru copii Avenli, cu inel gonflabil, strat triplu PVC, 366 x 76cm, capacitate 5377 L 40183 -99 413.22 450.40 Y
1128289 Set perne decorative pentru mobilier paleti,perna sezut 120x70 cm + perna spate 120x40 cm, culoare bej 37046 0 0.00 19.00 Y
687122 Hamac Brazilian tip Scaun Deluxe pentru Casa, Curte sau Gradina, Capacitate 120kg, multicolor 36416 -99 77.86 93.03 Y
1129605 Set perne decorative pentru mobilier paleti, perna sezut 120x70 cm + perna spate 120x40 cm culoare galben 35731 0 0.00 19.00 Y
897024 Costum de Mos Craciun pentru adulti, 5 piese,material flausat 35474 -99 42.92 45.99 Y
447588 Arc curcubeu jocul copilariei multicolor cu particule de sclipici 35219 -99 1.90 18.00 Y
1274272 Sistem de incalzire covoras solar pentru apa din piscina, 120 x 120 cm 34381 -99 451.12 515.39 Y
481220 Lantisor Dublu Colier Auriu Elegant, Lungime Reglabila 33274 -99 2.19 7.00 Y
1080078 Cooler laptop 9-17", reglabil, 5 ventilatoare, 2xusb, cu ecran LCD, negru 33136 -99 65.12 78.14 Y
596382 Suport numar inmatriculare auto carbon Kft Auto 32608 -99 0.00 0.00 N
444124 Noptiera cu 2 sertare, model Karo K2, culoare stejar 31317 -99 114.49 118.00 Y
528832 Set Trenulet Educational din Lemn Format din 18 Elemente Colorate pentru Copii 30497 -99 55.16 62.00 Y
697795 Abtibild Cromat litere / cifre / semne 3D ManiaCars 30330 -99 1.36 0.00 N