How to select unique years from field with Date type?

Question

SQL

How to select unique years from field with Date type?

Answer 1

select datepart(yyyy, dtField) from table group by datepart(yyyy, dtField) having count(*)=1

Answer 2

SELECT DATE_FORMAT(e.start, '%y') AS year FROM events e GROUP BY year;

Answer 3

SELECT DISTINCT(DATE_FORMAT(e.start, '%Y')) AS year FROM events e

Answer 4

select distinct year(dat) from table