after executing explain in mysql client, the result is:
mysql> explain select * from tbl_demo;
+-----------+------------------------+
| DATA_NODE | SQL |
+-----------+------------------------+
| dn1 | select * from tbl_demo |
+-----------+------------------------+
1 row in set (0.00 sec)
can't find id, select_type, table, key, ref, rows and Extra column why?