SELECT 
  SQL_CALC_FOUND_ROWS products.product_id, 
  IF(
    shared_descr.product_id IS NOT NULL, 
    shared_descr.product, descr1.product
  ) as product, 
  companies.company as company_name, 
  products.product_type, 
  products.parent_product_id 
FROM 
  cscart_products as products 
  INNER JOIN cscart_product_features_values as c_var ON c_var.product_id = products.product_id 
  AND c_var.lang_code = 'ru' 
  AND c_var.variant_id = 6840 
  LEFT JOIN cscart_product_descriptions as descr1 ON descr1.product_id = products.product_id 
  AND descr1.lang_code = 'ru' 
  LEFT JOIN cscart_product_prices as prices ON prices.product_id = products.product_id 
  AND prices.lower_limit = 1 
  LEFT JOIN cscart_companies AS companies ON companies.company_id = products.company_id 
  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') 
  AND cscart_categories.storefront_id IN (0, 1) 
  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 = 'ru' 
WHERE 
  1 
  AND companies.status IN ('A') 
  AND (
    products.amount > 0 
    OR products.tracking = 'D'
  ) 
  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 products.parent_product_id = 0 
GROUP BY 
  products.product_id 
ORDER BY 
  product asc, 
  products.product_id ASC 
LIMIT 
  0, 20

Query time 0.00257

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "37.51"
    },
    "ordering_operation": {
      "using_filesort": true,
      "grouping_operation": {
        "using_temporary_table": true,
        "using_filesort": false,
        "nested_loop": [
          {
            "table": {
              "table_name": "companies",
              "access_type": "system",
              "possible_keys": [
                "PRIMARY"
              ],
              "rows_examined_per_scan": 1,
              "rows_produced_per_join": 1,
              "filtered": "100.00",
              "cost_info": {
                "read_cost": "0.00",
                "eval_cost": "0.10",
                "prefix_cost": "0.00",
                "data_read_per_join": "5K"
              },
              "used_columns": [
                "company_id",
                "status",
                "company"
              ]
            }
          },
          {
            "table": {
              "table_name": "c_var",
              "access_type": "ref",
              "possible_keys": [
                "variant_id",
                "lang_code",
                "product_id",
                "idx_product_feature_variant_id"
              ],
              "key": "variant_id",
              "used_key_parts": [
                "variant_id"
              ],
              "key_length": "3",
              "ref": [
                "const"
              ],
              "rows_examined_per_scan": 27,
              "rows_produced_per_join": 26,
              "filtered": "99.57",
              "cost_info": {
                "read_cost": "3.20",
                "eval_cost": "2.69",
                "prefix_cost": "5.90",
                "data_read_per_join": "20K"
              },
              "used_columns": [
                "product_id",
                "variant_id",
                "lang_code"
              ],
              "attached_condition": "(`zdrowy_db`.`c_var`.`lang_code` = 'ru')"
            }
          },
          {
            "table": {
              "table_name": "products",
              "access_type": "eq_ref",
              "possible_keys": [
                "PRIMARY",
                "status",
                "idx_parent_product_id"
              ],
              "key": "PRIMARY",
              "used_key_parts": [
                "product_id"
              ],
              "key_length": "3",
              "ref": [
                "zdrowy_db.c_var.product_id"
              ],
              "rows_examined_per_scan": 1,
              "rows_produced_per_join": 1,
              "filtered": "5.00",
              "cost_info": {
                "read_cost": "6.72",
                "eval_cost": "0.13",
                "prefix_cost": "15.31",
                "data_read_per_join": "11K"
              },
              "used_columns": [
                "product_id",
                "product_type",
                "status",
                "company_id",
                "amount",
                "usergroup_ids",
                "tracking",
                "parent_product_id"
              ],
              "attached_condition": "((`zdrowy_db`.`products`.`company_id` = '1') and (`zdrowy_db`.`products`.`parent_product_id` = 0) and ((`zdrowy_db`.`products`.`amount` > 0) or (`zdrowy_db`.`products`.`tracking` = 'D')) and ((`zdrowy_db`.`products`.`usergroup_ids` = '') or (0 <> find_in_set(0,`zdrowy_db`.`products`.`usergroup_ids`)) or (0 <> find_in_set(1,`zdrowy_db`.`products`.`usergroup_ids`))) and (`zdrowy_db`.`products`.`status` = 'A'))"
            }
          },
          {
            "table": {
              "table_name": "products_categories",
              "access_type": "ref",
              "possible_keys": [
                "PRIMARY",
                "pt"
              ],
              "key": "pt",
              "used_key_parts": [
                "product_id"
              ],
              "key_length": "3",
              "ref": [
                "zdrowy_db.c_var.product_id"
              ],
              "rows_examined_per_scan": 20,
              "rows_produced_per_join": 26,
              "filtered": "100.00",
              "cost_info": {
                "read_cost": "6.72",
                "eval_cost": "2.69",
                "prefix_cost": "24.72",
                "data_read_per_join": "430"
              },
              "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": [
                "zdrowy_db.products_categories.category_id"
              ],
              "rows_examined_per_scan": 1,
              "rows_produced_per_join": 1,
              "filtered": "5.00",
              "cost_info": {
                "read_cost": "6.72",
                "eval_cost": "0.13",
                "prefix_cost": "34.13",
                "data_read_per_join": "8K"
              },
              "used_columns": [
                "category_id",
                "usergroup_ids",
                "status",
                "storefront_id"
              ],
              "attached_condition": "(((`zdrowy_db`.`cscart_categories`.`usergroup_ids` = '') or (0 <> find_in_set(0,`zdrowy_db`.`cscart_categories`.`usergroup_ids`)) or (0 <> find_in_set(1,`zdrowy_db`.`cscart_categories`.`usergroup_ids`))) and (`zdrowy_db`.`cscart_categories`.`status` in ('A','H')) and (`zdrowy_db`.`cscart_categories`.`storefront_id` in (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": [
                "zdrowy_db.c_var.product_id",
                "const",
                "const"
              ],
              "rows_examined_per_scan": 1,
              "rows_produced_per_join": 1,
              "filtered": "100.00",
              "cost_info": {
                "read_cost": "0.02",
                "eval_cost": "0.13",
                "prefix_cost": "34.28",
                "data_read_per_join": "6K"
              },
              "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": [
                "zdrowy_db.c_var.product_id",
                "const"
              ],
              "rows_examined_per_scan": 1,
              "rows_produced_per_join": 1,
              "filtered": "100.00",
              "cost_info": {
                "read_cost": "0.02",
                "eval_cost": "0.13",
                "prefix_cost": "34.43",
                "data_read_per_join": "7K"
              },
              "used_columns": [
                "product_id",
                "lang_code",
                "product"
              ]
            }
          },
          {
            "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": [
                "zdrowy_db.c_var.product_id"
              ],
              "rows_examined_per_scan": 19,
              "rows_produced_per_join": 25,
              "filtered": "99.33",
              "using_index": true,
              "cost_info": {
                "read_cost": "0.52",
                "eval_cost": "2.54",
                "prefix_cost": "37.51",
                "data_read_per_join": "608"
              },
              "used_columns": [
                "product_id",
                "lower_limit",
                "usergroup_id"
              ],
              "attached_condition": "((`zdrowy_db`.`prices`.`lower_limit` = 1) and (`zdrowy_db`.`prices`.`usergroup_id` in (0,0,1)))"
            }
          }
        ]
      }
    }
  }
}