SELECT 
  product_id 
FROM 
  cscart_mb_ali_products 
WHERE 
  product_id IN (
    20861, 20862, 20863, 20864, 20865, 20866, 
    20867, 20868, 20869, 20870, 20871, 
    20872, 20873, 20874, 20875, 20876
  )

Query time 0.00014

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_mb_ali_products",
      "access_type": "range",
      "possible_keys": ["product_id"],
      "key": "product_id",
      "key_length": "4",
      "used_key_parts": ["product_id"],
      "rows": 16,
      "filtered": 100,
      "attached_condition": "cscart_mb_ali_products.product_id in (20861,20862,20863,20864,20865,20866,20867,20868,20869,20870,20871,20872,20873,20874,20875,20876)",
      "using_index": true
    }
  }
}