SELECT 
  cscart_products.* 
FROM 
  cscart_products 
WHERE 
  cscart_products.product_id IN (
    400915, 400918, 391024, 400919, 390991, 
    390990, 390992, 390975, 391011, 391010, 
    391025, 390985
  )

Query time 0.00042

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost": 0.0216566,
    "nested_loop": [
      {
        "table": {
          "table_name": "cscart_products",
          "access_type": "range",
          "possible_keys": ["PRIMARY"],
          "key": "PRIMARY",
          "key_length": "3",
          "used_key_parts": ["product_id"],
          "loops": 1,
          "rows": 12,
          "cost": 0.0216566,
          "filtered": 100,
          "attached_condition": "cscart_products.product_id in (400915,400918,391024,400919,390991,390990,390992,390975,391011,391010,391025,390985)"
        }
      }
    ]
  }
}