SELECT 
  cscart_products.*, 
  cscart_products.ebay_status, 
  cscart_products.ebay_template_id 
FROM 
  cscart_products 
WHERE 
  cscart_products.product_id IN (
    20685, 20686, 20687, 20688, 20689, 20690, 
    20691, 20692, 20693, 20694, 20695, 
    20696, 20697, 20698, 20699, 20700
  )

Query time 0.00032

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 (20685,20686,20687,20688,20689,20690,20691,20692,20693,20694,20695,20696,20697,20698,20699,20700)"
    }
  }
}