As I told in my previous posts you can apply better way Date functions to work with dates. This special post I am explaining to apply on numeric date.
TRUNC ( PERIODIC_DATE, YEAR)
The TRUNC function truncates date to year. That means it gets date to yyyy- 01-01 from the input PERIODIC_DATE.
This function most frequently being used in data warehousing projects.
This is one of the best way to work with Date related functions.