Describe the bug

When using Python Mysqldb library to execute sql on Doris. Some time it will throw
error:

Commands out of sync; you can't run this command now

To Reproduce

1. Execute sql like:

execute("insert into table tbl1 select * from tbl2;")

Notice that there is a ; at the end of the statement.

1. If the insert statement has some warnings, then the error will throw.