SELECT 
  cscart_products.* 
FROM 
  cscart_products 
WHERE 
  cscart_products.product_id IN (
    1821, 1809, 1808, 1814, 1813, 1812, 1811, 
    1810, 1807, 1806, 1794, 1805
  )

Query time 0.00091

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": 12,
      "filtered": 100,
      "index_condition": "cscart_products.product_id in (1821,1809,1808,1814,1813,1812,1811,1810,1807,1806,1794,1805)"
    }
  }
}