Variables: how to conditionally add trailing comma

[sknaumov]

• What Grafana version and what operating system are you using?
  v10.4.2, Linux

• What are you trying to achieve?
  Group rows by columns specified in Grafana’s custom multi-value variable.

• How are you trying to achieve it?

SELECT
    ${group_by:doublequote},
    ...
GROUP BY
    ${group_by:doublequote},
    ...

• What happened?
  Everything works as expected except in a case when no group_by values are selected.
  In this case I have "", which is not a valid SQL.

• What did you expect to happen?
  Have a possibility to conditionally add trailing comma to variable expansion - either by some filter or by templating like $(if ) in Makefiles:

${group_by:doublequotescomma} -> "foo","bar",
${group_by:doublequotescomma} -> "foo",
${group_by:doublequotescomma} ->                    // nothing at all


${if $group_by,${group_by:doublequotes} + ",",}

If there are no means for it in Grafana, then probably someone could point me how to overcome this limitation using SQL?

[yosiasz]

do an if statement in the query section to check value of $group_by proper postgresql if statement
I made the All value -1