Splunk DB Connect 3.1.1 - Why database input for MS SQL server query does not capture any data to the index?

[nbtsplunk]

i have setup a database input to connect to MS SQL server in Splunk DB connect 3.1.1. My database connection is working fine and I just tested a simple query like "select * from " but no data has been collected and indexed in my new index. i did not see any errors from any log.

Below is the setting in db_inputs.conf but i have configured it through the GUI.

[data-SQL]
connection = data-SQLconnection
disabled = 0
host = data-SQL
index = av
index_time_mode = current
interval = 60
mode = batch
query = SELECT * from

source = data-SQL
sourcetype = data:sql

i appreciate for any advices.
Thanks