SELECT 
  cscart_products.* 
FROM 
  cscart_products 
WHERE 
  cscart_products.product_id IN (
    18672, 18674, 18681, 19112, 20050, 20021, 
    18678, 18677, 18680, 18685, 18688, 
    18723
  )

Query time 0.00059

JSON explain

{
  "query_block": {
    "select_id": 1,
    "nested_loop": [
      {
        "table": {
          "table_name": "cscart_products",
          "access_type": "range",
          "possible_keys": ["PRIMARY"],
          "key": "PRIMARY",
          "key_length": "3",
          "used_key_parts": ["product_id"],
          "rows": 12,
          "filtered": 100,
          "index_condition": "cscart_products.product_id in (18672,18674,18681,19112,20050,20021,18678,18677,18680,18685,18688,18723)"
        }
      }
    ]
  }
}