Merge pull request #114902 from sidramadoss/patch-72

Update sql-reference-data.md

Author: PRMerger13

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

@@ -150,16 +150,16 @@ When using the delta query, [temporal tables in Azure SQL Database](../sql-datab
 
 2. Author the delta query. 
 
-   This query retrieves all of the rows in your SQL database that were inserted or deleted within a start time, **\@deltaStartTime**, and an end time **\@deltaEndTime**. The delta query must return the same columns as the snapshot query, as well as the column **_operation_**. This column defines if the row is inserted or deleted between **\@deltaStartTime** and **\@deltaEndTime**. The resulting rows are flagged as **1** if the records were inserted, or **2** if deleted. 
+   This query retrieves all of the rows in your SQL database that were inserted or deleted within a start time, **\@deltaStartTime**, and an end time **\@deltaEndTime**. The delta query must return the same columns as the snapshot query, as well as the column **_operation_**. This column defines if the row is inserted or deleted between **\@deltaStartTime** and **\@deltaEndTime**. The resulting rows are flagged as **1** if the records were inserted, or **2** if deleted. The query must also add **watermark** from the SQL Server side to ensure all the updates in the delta period are captured appropriately. Using delta query without **watermark** may result in incorrect reference dataset.  
 
    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, 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, 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
    ```