pers_upn_unknown possible enhancement populating from pers_upn for UN1-10 codes

[robjharrison]

Changed Script 2: populate_ssd_person.sql (BUG 14801)

2.1 pers_upn_unkown
Now the script always put NULL to pers_upn_unknown. In Merton, we store UN1 - UN10 in pers_upn field for unknown UPN cases.
So we modified the script to check if UN1 - UN10 are in pers_upn, we will copy this value to pers_upn_unknown.

Flagged by: Merton.

[robjharrison]

This would/could likely be applicable to the wider pilot LAs. Will Implementing into the populate staging scripts