SELECT 
  b.row_position 
FROM 
  (
    SELECT 
      product_id, 
      @r := @r + 1 as row_position 
    FROM 
      (
        SELECT 
          products.product_id 
        FROM 
          cscart_products as products 
          LEFT JOIN cscart_product_descriptions as descr1 ON descr1.product_id = products.product_id 
          AND descr1.lang_code = 'en' 
          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 = 'en' 
          LEFT JOIN cscart_product_popularity as popularity ON popularity.product_id = products.product_id 
        WHERE 
          1 
          AND cscart_categories.category_id IN (653) 
          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) 
        GROUP BY 
          products.product_id 
        ORDER BY 
          descr1.product asc
      ) AS a
  ) AS b 
WHERE 
  b.product_id = 981

Query time 0.00067

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "<derived2>",
      "access_type": "ALL",
      "rows": 4,
      "filtered": 100,
      "attached_condition": "b.product_id = 981",
      "materialized": {
        "query_block": {
          "select_id": 2,
          "table": {
            "table_name": "<derived3>",
            "access_type": "ALL",
            "rows": 4,
            "filtered": 100,
            "materialized": {
              "query_block": {
                "select_id": 3,
                "filesort": {
                  "sort_key": "descr1.product",
                  "temporary_table": {
                    "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": 4,
                      "filtered": 100,
                      "attached_condition": "products_categories.category_id <=> 653",
                      "using_index": true
                    },
                    "table": {
                      "table_name": "products",
                      "access_type": "eq_ref",
                      "possible_keys": ["PRIMARY", "status"],
                      "key": "PRIMARY",
                      "key_length": "3",
                      "used_key_parts": ["product_id"],
                      "ref": ["rfswire_cart.products_categories.product_id"],
                      "rows": 1,
                      "filtered": 87.96884918,
                      "attached_condition": "(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": "descr1",
                      "access_type": "eq_ref",
                      "possible_keys": ["PRIMARY", "product_id"],
                      "key": "PRIMARY",
                      "key_length": "9",
                      "used_key_parts": ["product_id", "lang_code"],
                      "ref": [
                        "rfswire_cart.products_categories.product_id",
                        "const"
                      ],
                      "rows": 1,
                      "filtered": 100,
                      "attached_condition": "trigcond(descr1.lang_code = 'en')"
                    },
                    "table": {
                      "table_name": "prices",
                      "access_type": "ref",
                      "possible_keys": [
                        "usergroup",
                        "product_id",
                        "lower_limit",
                        "usergroup_id"
                      ],
                      "key": "product_id",
                      "key_length": "3",
                      "used_key_parts": ["product_id"],
                      "ref": ["rfswire_cart.products_categories.product_id"],
                      "rows": 1,
                      "filtered": 64.24570465,
                      "attached_condition": "prices.lower_limit = 1 and prices.usergroup_id in (0,0,1)"
                    }
                  }
                }
              }
            }
          }
        }
      }
    }
  }
}