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Last tested: Jan 16, 2019
According to docs, the sql_trigger_value will only consider the first row and column in the SQL you write. It is recommended to have your trigger value return only 1 value, to prevent confusion and protect non-streaming SQL dialects from loading large result sets into memory.
If you really want more than 1 column considered by your sql trigger value, you can concatenate the columns, which will cause it to trigger if there is a change in any of these columns.