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, 
  cscart_categories.position AS category_position, 
  products_categories.category_id 
FROM 
  cscart_products as products 
  LEFT JOIN cscart_product_features_values as var_val_18 ON var_val_18.product_id = products.product_id 
  AND var_val_18.lang_code = 'ja' 
  AND var_val_18.feature_id = 18 
  LEFT JOIN cscart_product_descriptions as descr1 ON descr1.product_id = products.product_id 
  AND descr1.lang_code = 'ja' 
  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 = 'ja' 
WHERE 
  1 
  AND (
    var_val_18.variant_id IN (136)
  ) 
  AND cscart_categories.category_id IN (259) 
  AND companies.status IN ('A') 
  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 
  category_position ASC, 
  category_id, 
  products_categories.position asc, 
  products.product_id ASC 
LIMIT 
  0, 50

Query time 0.00090

JSON explain

{
  "query_block": {
    "select_id": 1,
    "filesort": {
      "sort_key": "products_categories.position, products.product_id",
      "temporary_table": {
        "table": {
          "table_name": "companies",
          "access_type": "system",
          "possible_keys": ["PRIMARY"],
          "rows": 1,
          "filtered": 100
        },
        "table": {
          "table_name": "cscart_categories",
          "access_type": "const",
          "possible_keys": ["PRIMARY", "c_status", "p_category_id"],
          "key": "PRIMARY",
          "key_length": "3",
          "used_key_parts": ["category_id"],
          "ref": ["const"],
          "rows": 1,
          "filtered": 100
        },
        "table": {
          "table_name": "products_categories",
          "access_type": "ref",
          "possible_keys": ["PRIMARY", "pt"],
          "key": "PRIMARY",
          "key_length": "3",
          "used_key_parts": ["category_id"],
          "ref": ["const"],
          "rows": 11,
          "filtered": 100,
          "attached_condition": "products_categories.category_id <=> 259"
        },
        "table": {
          "table_name": "products",
          "access_type": "eq_ref",
          "possible_keys": ["PRIMARY", "status"],
          "key": "PRIMARY",
          "key_length": "3",
          "used_key_parts": ["product_id"],
          "ref": ["markins_test.products_categories.product_id"],
          "rows": 1,
          "filtered": 60.5678215,
          "attached_condition": "products.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` = 'A'"
        },
        "table": {
          "table_name": "shared_descr",
          "access_type": "eq_ref",
          "possible_keys": ["PRIMARY", "product_id", "company_id"],
          "key": "PRIMARY",
          "key_length": "13",
          "used_key_parts": ["product_id", "lang_code", "company_id"],
          "ref": ["markins_test.products_categories.product_id", "const", "const"],
          "rows": 1,
          "filtered": 100,
          "attached_condition": "trigcond(shared_descr.lang_code = 'ja')"
        },
        "table": {
          "table_name": "var_val_18",
          "access_type": "eq_ref",
          "possible_keys": [
            "PRIMARY",
            "fl",
            "variant_id",
            "lang_code",
            "product_id",
            "fpl",
            "idx_product_feature_variant_id"
          ],
          "key": "PRIMARY",
          "key_length": "15",
          "used_key_parts": ["feature_id", "product_id", "variant_id", "lang_code"],
          "ref": [
            "const",
            "markins_test.products_categories.product_id",
            "const",
            "const"
          ],
          "rows": 1,
          "filtered": 95.54895782,
          "attached_condition": "var_val_18.lang_code = 'ja'",
          "using_index": true
        },
        "table": {
          "table_name": "descr1",
          "access_type": "eq_ref",
          "possible_keys": ["PRIMARY", "product_id"],
          "key": "PRIMARY",
          "key_length": "9",
          "used_key_parts": ["product_id", "lang_code"],
          "ref": ["markins_test.products_categories.product_id", "const"],
          "rows": 1,
          "filtered": 100,
          "attached_condition": "trigcond(descr1.lang_code = 'ja')"
        },
        "table": {
          "table_name": "prices",
          "access_type": "ref",
          "possible_keys": [
            "usergroup",
            "product_id",
            "lower_limit",
            "usergroup_id"
          ],
          "key": "usergroup",
          "key_length": "3",
          "used_key_parts": ["product_id"],
          "ref": ["markins_test.products_categories.product_id"],
          "rows": 2,
          "filtered": 56.08769226,
          "attached_condition": "prices.lower_limit = 1 and prices.usergroup_id in (0,0,1)",
          "using_index": true
        }
      }
    }
  }
}