Returns the portion of the first Period expression that exists before the beginning of the second Period expression when the Period expressions overlap.
When the Period expressions overlap but there is no portion of the first Period expression before the beginning of the second Period expression or the Period expressions do not overlap, the function returns NULL. If either Period expression is NULL, LDIFF returns NULL.
period_expression LDIFF period_expression
Any expression that evaluates to a Period data type.
The Period expression must be comparable with the other expression. Implicit casting to a Period data type is not supported.