SELECT 
  product_id 
FROM 
  cscart_mb_ali_products 
WHERE 
  product_id IN (
    21245, 21246, 21247, 21248, 21249, 21250, 
    21251, 21252, 21253, 21254, 21255, 
    21256, 21257, 21258, 21259, 21260
  )

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 (21245,21246,21247,21248,21249,21250,21251,21252,21253,21254,21255,21256,21257,21258,21259,21260)",
      "using_index": true
    }
  }
}