SELECT 
  cscart_products.* 
FROM 
  cscart_products 
WHERE 
  cscart_products.product_id IN (
    104, 376, 390, 511, 512, 513, 514, 1612, 
    1613, 1614, 1615, 1616, 1617, 1618, 
    1628, 5476
  )

Query time 0.00077

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_products",
      "access_type": "range",
      "possible_keys": ["PRIMARY"],
      "key": "PRIMARY",
      "key_length": "3",
      "used_key_parts": ["product_id"],
      "rows": 16,
      "filtered": 100,
      "index_condition": "cscart_products.product_id in (104,376,390,511,512,513,514,1612,1613,1614,1615,1616,1617,1618,1628,5476)"
    }
  }
}