Fix sql ref data watermark name + missing comma

Author: xindzhan

articles/stream-analytics/sql-reference-data.md

@@ -155,11 +155,11 @@ When using the delta query, [temporal tables in Azure SQL Database](../sql-datab
    For records that were updated, the temporal table does bookkeeping by capturing an insertion and deletion operation. The Stream Analytics runtime will then apply the results of the delta query to the previous snapshot to keep the reference data up to date. An example of delta query is show below:
 
    ```SQL
-      SELECT DeviceId, GroupDeviceId, Description, ValidFrom as watermark 1 as _operation_
+      SELECT DeviceId, GroupDeviceId, Description, ValidFrom as _watermark_, 1 as _operation_
       FROM dbo.DeviceTemporal
       WHERE ValidFrom BETWEEN @deltaStartTime AND @deltaEndTime   -- records inserted
       UNION
-      SELECT DeviceId, GroupDeviceId, Description, ValidTo as watermark 2 as _operation_
+      SELECT DeviceId, GroupDeviceId, Description, ValidTo as _watermark_, 2 as _operation_
       FROM dbo.DeviceHistory   -- table we created in step 1
       WHERE ValidTo BETWEEN @deltaStartTime AND @deltaEndTime     -- record deleted
    ```