max(ts) 和 max(cast(ts as decimal(38,8))) 为什么结果不同呢

[colagy]

mysql> select max(ts) as ts from ods_api_jstqm_sale_order_info_f;;
±-----------+
| ts |
±-----------+
| 9999999863 |
±-----------+
1 row in set (0.04 sec)

ERROR:
No query specified

mysql> select max(cast(ts as decimal(38,8))) as ts from ods_api_jstqm_sale_order_info_f;
±---------------------+
| ts |
±---------------------+
| 11548071380.00000000 |
±---------------------+
1 row in set (0.07 sec)