SELECT 
  product_id 
FROM 
  cscart_mb_ali_products 
WHERE 
  product_id IN (
    21903, 21904, 21905, 21906, 21907, 21908, 
    21909, 21910, 21911, 21912, 21913, 
    21914, 21915, 21916, 21917, 21918
  )

Query time 0.00018

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 (21903,21904,21905,21906,21907,21908,21909,21910,21911,21912,21913,21914,21915,21916,21917,21918)",
      "using_index": true
    }
  }
}