LDIFF is used to find the left difference of the first Period expression with the second Period expression.
SELECT ename, period2 LDIFF period1 FROM employee;
Assume the query runs on the following employee table where period1 and period2 are PERIOD(DATE) columns:
ename period1 period2
----- ---------------------------- ----------------------------
Adams ('2005-02-03', '2006-02-03') ('2005-02-03', '2006-02-03')
Mary ('2005-04-02', '2006-01-03') ('2005-02-03', '2006-02-03')
Jones ('2004-01-02', '2004-03-05') ('2002-03-05', '2004-10-07')
Randy ('2006-01-02', '2007-03-05') ('2004-03-07', '2005-10-07')
Simon ? ('2005-02-03', '2005-07-27')
The result is:
ename (period2 LDIFF period1)
----- ----------------------------
Adams ?
Mary ('2005-02-03', '2005-04-02')
Jones ('2002-03-05', '2004-01-02')
Randy ?
Simon ?