SELECT 
  cscart_products.* 
FROM 
  cscart_products 
WHERE 
  cscart_products.product_id IN (
    391010, 391025, 390985, 390996, 390997, 
    391012, 400920, 391000, 391001, 391020, 
    461008, 390989
  )

Query time 0.00037

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 (391010,391025,390985,390996,390997,391012,400920,391000,391001,391020,461008,390989)"
        }
      }
    ]
  }
}