SELECT 
  SQL_CALC_FOUND_ROWS products.product_id, 
  IF(
    shared_descr.product_id IS NOT NULL, 
    shared_descr.product, descr1.product
  ) as product, 
  SUM(
    cscart_also_bought_products.amount
  ) amnt, 
  IF(
    products.age_verification = 'Y', 
    'Y', 
    IF(
      cscart_categories.age_verification = 'Y', 
      'Y', cscart_categories.parent_age_verification
    )
  ) as need_age_verification, 
  IF(
    products.age_limit > cscart_categories.age_limit, 
    IF(
      products.age_limit > cscart_categories.parent_age_limit, 
      products.age_limit, cscart_categories.parent_age_limit
    ), 
    IF(
      cscart_categories.age_limit > cscart_categories.parent_age_limit, 
      cscart_categories.age_limit, cscart_categories.parent_age_limit
    )
  ) as age_limit 
FROM 
  cscart_products as products 
  LEFT JOIN cscart_product_descriptions as descr1 ON descr1.product_id = products.product_id 
  AND descr1.lang_code = 'no' 
  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 = 1 
  AND shared_descr.lang_code = 'no' 
  LEFT JOIN cscart_also_bought_products ON cscart_also_bought_products.related_id = products.product_id 
WHERE 
  1 
  AND cscart_categories.company_id = 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) 
  AND cscart_also_bought_products.product_id = 1936 
GROUP BY 
  cscart_also_bought_products.related_id 
ORDER BY 
  SUM(
    cscart_also_bought_products.amount
  ) desc, 
  products.product_id ASC 
LIMIT 
  0, 12

Query time 0.00805

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "272.70"
    },
    "ordering_operation": {
      "using_filesort": true,
      "grouping_operation": {
        "using_temporary_table": true,
        "using_filesort": false,
        "nested_loop": [
          {
            "table": {
              "table_name": "cscart_also_bought_products",
              "access_type": "ref",
              "possible_keys": [
                "PRIMARY"
              ],
              "key": "PRIMARY",
              "used_key_parts": [
                "product_id"
              ],
              "key_length": "3",
              "ref": [
                "const"
              ],
              "rows_examined_per_scan": 27,
              "rows_produced_per_join": 27,
              "filtered": "100.00",
              "index_condition": "((`eshopuga_upgr_4122`.`cscart_also_bought_products`.`related_id` is not null) and (`eshopuga_upgr_4122`.`cscart_also_bought_products`.`related_id` is not null))",
              "cost_info": {
                "read_cost": "27.00",
                "eval_cost": "5.40",
                "prefix_cost": "32.40",
                "data_read_per_join": "432"
              },
              "used_columns": [
                "product_id",
                "related_id",
                "amount"
              ]
            }
          },
          {
            "table": {
              "table_name": "products",
              "access_type": "eq_ref",
              "possible_keys": [
                "PRIMARY",
                "status"
              ],
              "key": "PRIMARY",
              "used_key_parts": [
                "product_id"
              ],
              "key_length": "3",
              "ref": [
                "eshopuga_upgr_4122.cscart_also_bought_products.related_id"
              ],
              "rows_examined_per_scan": 1,
              "rows_produced_per_join": 24,
              "filtered": "91.44",
              "cost_info": {
                "read_cost": "27.00",
                "eval_cost": "4.94",
                "prefix_cost": "64.80",
                "data_read_per_join": "147K"
              },
              "used_columns": [
                "product_id",
                "status",
                "usergroup_ids",
                "age_verification",
                "age_limit"
              ],
              "attached_condition": "(((`eshopuga_upgr_4122`.`products`.`usergroup_ids` = '') or find_in_set(0,`eshopuga_upgr_4122`.`products`.`usergroup_ids`) or find_in_set(1,`eshopuga_upgr_4122`.`products`.`usergroup_ids`)) and (`eshopuga_upgr_4122`.`products`.`status` = 'A'))"
            }
          },
          {
            "table": {
              "table_name": "prices",
              "access_type": "ref",
              "possible_keys": [
                "usergroup",
                "product_id",
                "lower_limit",
                "usergroup_id"
              ],
              "key": "usergroup",
              "used_key_parts": [
                "product_id"
              ],
              "key_length": "3",
              "ref": [
                "eshopuga_upgr_4122.cscart_also_bought_products.related_id"
              ],
              "rows_examined_per_scan": 1,
              "rows_produced_per_join": 24,
              "filtered": "99.83",
              "using_index": true,
              "cost_info": {
                "read_cost": "24.69",
                "eval_cost": "4.93",
                "prefix_cost": "94.43",
                "data_read_per_join": "591"
              },
              "used_columns": [
                "product_id",
                "lower_limit",
                "usergroup_id"
              ],
              "attached_condition": "((`eshopuga_upgr_4122`.`prices`.`lower_limit` = 1) and (`eshopuga_upgr_4122`.`prices`.`usergroup_id` in (0,0,1)))"
            }
          },
          {
            "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": [
                "eshopuga_upgr_4122.cscart_also_bought_products.related_id",
                "const",
                "const"
              ],
              "rows_examined_per_scan": 1,
              "rows_produced_per_join": 24,
              "filtered": "100.00",
              "cost_info": {
                "read_cost": "24.65",
                "eval_cost": "4.93",
                "prefix_cost": "124.00",
                "data_read_per_join": "93K"
              },
              "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": [
                "eshopuga_upgr_4122.cscart_also_bought_products.related_id",
                "const"
              ],
              "rows_examined_per_scan": 1,
              "rows_produced_per_join": 24,
              "filtered": "100.00",
              "cost_info": {
                "read_cost": "24.65",
                "eval_cost": "4.93",
                "prefix_cost": "153.58",
                "data_read_per_join": "94K"
              },
              "used_columns": [
                "product_id",
                "lang_code",
                "product"
              ]
            }
          },
          {
            "table": {
              "table_name": "cscart_categories",
              "access_type": "ALL",
              "possible_keys": [
                "PRIMARY",
                "c_status",
                "p_category_id"
              ],
              "rows_examined_per_scan": 115,
              "rows_produced_per_join": 56,
              "filtered": "2.00",
              "using_join_buffer": "Block Nested Loop",
              "cost_info": {
                "read_cost": "39.77",
                "eval_cost": "11.34",
                "prefix_cost": "204.68",
                "data_read_per_join": "151K"
              },
              "used_columns": [
                "category_id",
                "company_id",
                "usergroup_ids",
                "status",
                "age_verification",
                "age_limit",
                "parent_age_verification",
                "parent_age_limit"
              ],
              "attached_condition": "((`eshopuga_upgr_4122`.`cscart_categories`.`company_id` = 1) and ((`eshopuga_upgr_4122`.`cscart_categories`.`usergroup_ids` = '') or find_in_set(0,`eshopuga_upgr_4122`.`cscart_categories`.`usergroup_ids`) or find_in_set(1,`eshopuga_upgr_4122`.`cscart_categories`.`usergroup_ids`)) and (`eshopuga_upgr_4122`.`cscart_categories`.`status` in ('A','H')))"
            }
          },
          {
            "table": {
              "table_name": "products_categories",
              "access_type": "eq_ref",
              "possible_keys": [
                "PRIMARY",
                "pt"
              ],
              "key": "PRIMARY",
              "used_key_parts": [
                "category_id",
                "product_id"
              ],
              "key_length": "6",
              "ref": [
                "eshopuga_upgr_4122.cscart_categories.category_id",
                "eshopuga_upgr_4122.cscart_also_bought_products.related_id"
              ],
              "rows_examined_per_scan": 1,
              "rows_produced_per_join": 56,
              "filtered": "100.00",
              "using_index": true,
              "cost_info": {
                "read_cost": "56.69",
                "eval_cost": "11.34",
                "prefix_cost": "272.70",
                "data_read_per_join": "906"
              },
              "used_columns": [
                "product_id",
                "category_id"
              ]
            }
          }
        ]
      }
    }
  }
}