LP#1802166: (follow-up) document a way to clear names from already-purged patron...

LP#1802166: (follow-up) document a way to clear names from already-purged patron records

For reference, the following SQL will clear the preferred name
and name keyword fields from already-purged records:

UPDATE actor.usr
SET pref_prefix = NULL,
    pref_first_given_name = NULL,
    pref_second_given_name = NULL,
    pref_family_name = NULL,
    pref_suffix = NULL,
    name_keywords = NULL
WHERE usrname ~ ('^' || id || '-PURGED')
AND NOT active
AND deleted
AND (
    pref_prefix IS NOT NULL OR
    pref_first_given_name IS NOT NULL OR
    pref_second_given_name IS NOT NULL OR
    pref_family_name IS NOT NULL OR
    pref_suffix IS NOT NULL OR
    name_keywords IS NOT NULL
);

Signed-off-by: Galen Charlton <gmc@equinoxinitiative.org>