ADD_YEARS takes a date, from either an information or in ISO8601 format, and a number of years to add, and returns a date with the given number of years added.
In the special case that the new year doesn't contain the original date (e.g. when adding a year to the leap day 29.02.2016) the new date will have the same number of days from the beginning of the year (e.g. 01.03.2017 in the earlier example).
This returns 2018-01-01T00:00:00, so the year 18 years after the 1st January 2000.
Example: Date with time
If you specify not just a date, but a date and time in ISO8601 format, the function includes the time in the calculation.
This returns also the 1st January 2018, but at 9:35:23, so 2018-01-01T09:35:23.