HELP: SQL and Singlestat, how to display the count of the selected rows?

Grafana Stat Panel
1

Hi, I’m getting crazy with a very basic query.

I’m connected to a SQL Server database and I would like to display the count of the selected rows in a Singlestat panel.

Unfortunately, among the option in the Value->Show configuration dropdown I do not find any ‘Count’ or similar option.

Snipaste_2019-12-20_15-38-43

I treid to include the COUNT funziont in the SELECT statement like here:

SELECT
  $__timeEpoch([EndTime]),
  [Operation] as metric,
  COUNT([ExLenght (m)]) as value
FROM
  table_sample
WHERE
  $__timeFilter([EndTime]) AND Status = 'Completed' AND [Operation] = 'INTERMEDIATE'

but Grafana gives me this error:

mssql: Column ‘table_sample.EndTime’ is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause.

Note that if I remove the COUNT and change the line to [ExLenght (m)]) as value the query works but obviously I do not get the Count of the values.

What I am doing wrong? Thanks for helping!
Giuseppe