suppose this scenario:
you have a source table and a destination table, you want to transfer rows from source table to destination table, so you can use simple data flow with OLE DB source and OLE DB Destination. but problem hits when destination table has few rows inside, and there is Unique Constraint in ID field of Destination table.
in this situation your data flow will fail, because when OLE DB Destination want to insert rows in destination table, it will got Unique Constraint error and it will raise Data Flow error, and this will prevent OLE DB Destination to insert any rows in table, even rows which hasn't equivalent key in destination !
So, a work around needed here to avoid failing package and only move rows which hasn't problem with unique constraint in destination table.
let me explain it with a sample here...




