I current have two tags: a query tag that returns either an empty dataset or one row with 8 columns, and a boolean expression tag that has the expression isNull(myQueryTag). I'd like to be able to use the expression tag and have an alarm on it so that when isNull returns 0, the alarm triggers. However, I think that the problem I'm running into is that when the query tag executes, it never actually returns NULL even if the dataset is empty, an empty dataset may be different than NULL as right now the query tag is showing Dataset[0R x 8C]. How can I adjust this to work better? Is there a different expression function I could use instead of isNull, or do I need to adjust the query tag?
len(myQueryTag) = 0 should work to alarm when the query returns no rows.
Correct, they are different.
I think you would only ever get Null back from a scalar query, but since you are expecting multiple rows you can't use that type of query.