Running a SP with partition in SQL Server - sql-server

Question

In a Stored Procedure we are using partition function. The job runs based on the period like '202001','202002' etc. For previous periods the SP was executed and now due to some data issues we are thinking to execute the SP for previous periods.
We are actually loading data into a Work Table and using partition we are switching data from Work table to main table
ALTER TABLE db_table_Work switch
TO db_table partition $PARTITION.db_table_PFPerPost(#PeriodKey);
If we execute the SP now again for past period, will it cause the data to insert again for existing rows? Or will it insert the newly updated data?

Answer 1

SWITCH will err if the target partition is not empty. Furthermore, the non-partitioned source table must have a check constraint on the partitioning column to ensure all rows fall within the target boundary.
If data will exist in the primary table partition during reprocessing, you'll need to ensure data in the replaced partition is not changed during reprocessing of previous periods to avoid data loss. If that is not possible, a MERGE is needed to insert/update/delete rows instead of the more efficient SWITCH.
Consider partitioning the work table using the same partition scheme as the target table to avoid the need for a check constraint. This will also facilitate moving the partition into the work table and switching back after reprocessing. Below is an example of this technique, which assumes it is acceptable for the primary table partition to be empty during reprocessing of the period:
--switch primary table partiton into work table for reprocessing
ALTER TABLE db_table
SWITCH PARTITION $PARTITION.db_table_PFPerPost(#PeriodKey)
TO db_table_Work PARTITION $PARTITION.db_table_PFPerPost(#PeriodKey);
--reprocess data here
--switch reprocessed data back into primary table
ALTER TABLE db_table_Work
SWITCH PARTITION $PARTITION.db_table_PFPerPost(#PeriodKey)
TO db_table PARTITION $PARTITION.db_table_PFPerPost(#PeriodKey);