Update data-flow-exists.md

Author: kromerm

articles/data-factory/data-flow-exists.md

@@ -9,7 +9,7 @@ ms.service: data-factory
 ms.subservice: data-flows
 ms.topic: conceptual
 ms.custom: synapse
-ms.date: 09/09/2021
+ms.date: 03/22/2022
 ---
 
 # Exists transformation in mapping data flow
@@ -43,6 +43,8 @@ To create a free-form expression that contains operators other than "and" and "e
 
 :::image type="content" source="media/data-flow/exists1.png" alt-text="Exists custom settings":::
 
+If you are building dynamic patterns in your data flows by using "late binding" of columns via schema drift, you can use the ```byName()``` expression function to use the exists transformation without hardcoding (i.e. early binding) the column names. Example: ```toString(byName('ProductNumber','source1')) == toString(byName('ProductNumber','source2'))```
+
 ## Broadcast optimization
 
 :::image type="content" source="media/data-flow/broadcast.png" alt-text="Broadcast Join":::