SELECT 
  cscart_products.* 
FROM 
  cscart_products 
WHERE 
  cscart_products.product_id IN (
    21666, 21667, 21668, 21669, 21670, 21672, 
    21673, 21674, 21675, 21676, 21677, 
    21678, 21679, 21680, 21681, 21682, 
    21683, 21684, 21685, 21686, 21687, 
    21688, 21689, 21690
  )

Query time 0.00068

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": 24,
          "filtered": 100,
          "index_condition": "cscart_products.product_id in (21666,21667,21668,21669,21670,21672,21673,21674,21675,21676,21677,21678,21679,21680,21681,21682,21683,21684,21685,21686,21687,21688,21689,21690)"
        }
      }
    ]
  }
}