Hi @Lintao Yu ,
I think you could use SQL to create separate files with delta only, will need to define a patter for file naming, then you can use Get Metadata object to get only files created since x time, last 4 hours for example. Another way you could take a look is creating event based or Tumbling windows trigger to handle every time you create a file into container for example.
here's the link for some related documentation:
https://video2.skills-academy.com/en-us/azure/data-factory/solution-template-copy-new-files-lastmodifieddate
https://video2.skills-academy.com/en-us/azure/data-factory/how-to-create-event-trigger
https://video2.skills-academy.com/en-us/azure/data-factory/how-to-create-tumbling-window-trigger
https://video2.skills-academy.com/en-us/azure/data-factory/control-flow-get-metadata-activity
Please let us know and/or vote in case the suggestion works for you!