SELECT 
  product_id 
FROM 
  cscart_product_popularity 
WHERE 
  product_id IN (
    51215, 51214, 51213, 51444, 51445, 51446, 
    51447
  )

Query time 0.00031

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "1.69"
    },
    "table": {
      "table_name": "cscart_product_popularity",
      "access_type": "range",
      "possible_keys": [
        "PRIMARY",
        "total"
      ],
      "key": "PRIMARY",
      "used_key_parts": [
        "product_id"
      ],
      "key_length": "3",
      "rows_examined_per_scan": 7,
      "rows_produced_per_join": 7,
      "filtered": "100.00",
      "using_index": true,
      "cost_info": {
        "read_cost": "0.99",
        "eval_cost": "0.70",
        "prefix_cost": "1.69",
        "data_read_per_join": "224"
      },
      "used_columns": [
        "product_id"
      ],
      "attached_condition": "(`test_uchur_k`.`cscart_product_popularity`.`product_id` in (51215,51214,51213,51444,51445,51446,51447))"
    }
  }
}