Last function have result after all data been delete.

[wsf1990]

Bug Description 使用delete from table 删除所有数据之后，使用 select last(*) from table依旧能够查出内容。 To Reproduce Steps to reproduce the behavior:

1. delete from table
2. select last(*) from table

Screenshots

Environment (please complete the following information):

• TDengine Version 3.0.0.0