SELECT 
  product_id 
FROM 
  cscart_mb_ali_products 
WHERE 
  product_id IN (
    21069, 21070, 21071, 21072, 21073, 21074, 
    21075, 21076, 21077, 21078, 21079, 
    21080, 21081, 21082, 21083, 21084
  )

Query time 0.00012

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 (21069,21070,21071,21072,21073,21074,21075,21076,21077,21078,21079,21080,21081,21082,21083,21084)",
      "using_index": true
    }
  }
}