SELECT 
  cscart_products.* 
FROM 
  cscart_products 
WHERE 
  cscart_products.product_id IN (
    21088, 20980, 21071, 21074, 21072, 21073, 
    21076, 21119, 21166, 21116, 21117, 
    21118, 21087, 21120, 21096, 21113, 
    21097, 21114, 21105, 21108, 21106, 
    21098, 21110, 21111
  )

Query time 0.00100

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": 24,
      "filtered": 100,
      "index_condition": "cscart_products.product_id in (21088,20980,21071,21074,21072,21073,21076,21119,21166,21116,21117,21118,21087,21120,21096,21113,21097,21114,21105,21108,21106,21098,21110,21111)"
    }
  }
}