SELECT 
  product_id 
FROM 
  cscart_product_popularity 
WHERE 
  product_id IN (
    396045, 396046, 396047, 396048, 396049, 
    396050
  )

Query time 0.00036

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "3.42"
    },
    "table": {
      "table_name": "cscart_product_popularity",
      "access_type": "range",
      "possible_keys": [
        "PRIMARY",
        "total"
      ],
      "key": "total",
      "used_key_parts": [
        "product_id"
      ],
      "key_length": "3",
      "rows_examined_per_scan": 6,
      "rows_produced_per_join": 6,
      "filtered": "100.00",
      "using_index": true,
      "cost_info": {
        "read_cost": "2.22",
        "eval_cost": "1.20",
        "prefix_cost": "3.42",
        "data_read_per_join": "192"
      },
      "used_columns": [
        "product_id"
      ],
      "attached_condition": "(`webmarco`.`cscart_product_popularity`.`product_id` in (396045,396046,396047,396048,396049,396050))"
    }
  }
}