If the PV of the deletion overlaps the PA of a row, only the portion of the row information that is valid during the overlap is deleted, effectively changing the valid-time period for the row:
DELETE FROM employee_vt FOR PORTION OF job_dur FROM DATE’2000-01-01’ TO DATE’2002-01-01’ WHERE ename=’Fred’; SELECT * FROM employee_vt WHERE ename=’Fred’; eid ename terms job_start job_end ---- ----- ----- ---------- ----------- 1004 Fred PW12 2002/02/01 2009/01/01 1004 Fred PW12 2010/01/01 9999/12/31 DELETE FROM employee_vt FOR PORTION OF job_dur FROM DATE’2008-05-05’ TO DATE’2009-05-05’ WHERE ename=’Fred’; SELECT * FROM employee_vt WHERE ename=’Fred’; eid ename terms job_start job_end ---- ----- ----- ---------- ----------- 1004 Fred PW12 2002/01/01 2008/05/05 1004 Fred PW12 2009/05/01 9999/12/31