Using an Aggregate Window in SAP HANA Smart Data Streaming

Add an Aggregate Window

1. Click on Aggregate in the Palette and drop onto canvas.

   

2. Rename the stream to AVG_TEMP by clicking on Aggregate symbol. Then press the Enter key.

   

3. Select the Connector in the Palette. Drag the connector from DEVICE_EVENTS Join to AVG_TEMP.

   

4. Click Add Column Expression f(x) by clicking on the icon shown below.

   

5. Click the Copy Columns from Input menu item to execute it. You can also press c.

   

6. Click Select All or you can press Alt+s. Uncheck DEVICE_EVENTS.EVENT_NAME, DEVICE_EVENTS.EVENT_DESCRIPTION and DEVICE_EVENTS.MACHINETYPE. Click OK.

   

7. Now we will create a window on the input to this aggregation. Expand the Inputs tab and right click on DEVICE_EVENTS.

   

8. Click the Keep Policy menu item to execute it. You can also press k.

   

9. Click Time and enter 30 seconds in the entry box. Click OK.

   

10. To define the GROUP BY clause, expand the tab by clicking on +.

    

11. Double-click on GROUP BY unassigned_group_by.

    

12. Select the entry DEVICE_EVENTS.MACHINEID by clicking on it. Click Add >> and then click OK.

    

13. Now we need to add a GROUP filter, since we only want to aggregate temperature readings. Click Add Group Clause { } icon shown below.

    

    Note that a GROUP FILTER filters the incoming events before aggregation. In this case, the filter will filter out “DOOR” and “POWER” events so that this element only process “TEMP” events.

14. Click the Group Filter Clause menu item to execute it. You can also press g.

    

15. Double-click on Group Filter 1.

    

16. Enter DEVICE_EVENTS.EVENT_NAME='TEMP' as the filter expression in the text box. You can use Ctrl+Space for content assist. Confirm your entry by pressing Enter.

    

17. Expand the Column Expressions tab to edit expressions.

    

18. Double-click on DEVICE_EVENTS.EVENT_TIME.

    

19. Edit the expression for EVENT_TIME. Change it to: last(DEVICE_EVENTS.EVENT_TIME). This will cause the aggregate values for the group to show the event time of the last event received in the group. Confirm your entry by pressing Enter.

    

20. Double click the name EVENT_VALUE and rename this column to AVG_TEMP by typing in the text field. Confirm your entry by pressing Enter.

    

21. Double-click on the expression for AVG_TEMP, which is currently set to DEVICE_EVENTS.EVENT_VALUE.

    

22. Edit this expression to compute an average. Also, since the value field is a string, before we can compute an average, we need to convert it to a number. Change the expression to: avg(to_decimal(DEVICE_EVENTS.EVENT_VALUE, 4, 2)). Confirm your entry by pressing Enter.

    

Next Steps

• Tutorials: Generating Alerts Using a Derived Window in SAP HANA Smart Data Streaming