Hi Atul, to begin with before you implement any purge strategy it would be important to have a valid backup and recovery strategy. I have seen quite a few cases where users decides to purse Datatable and ValueStream/Stream entries and they end up purging more than needed and then there's no Ctrl + Z. So to begin with it would be strongly recommended to have backup and restore strategy if one is not already in place.
As to the purging if you are absolutely sure that the data in there and is not needed and you want to have some sort of automated purge keeping just a month's data you may want to look into implementing your own Scheduler Thing which will execute deletion of table entries based on the data and time or other constraint as you wish to add to that service. There's out of the box service available for deleting the data from the DataTable or the ValueStream/Streams
So what would be better/efficient approach for purging table DataTable:-
Execute delete-sql script directly on database table (DataTable) OR
Use Thingworx API to do so
As you had mentioned "There's out of the box service available for deleting the data from the DataTable or the ValueStream/Streams". Could you share some (and if any community/support/documentation link for the same)