how to compare year from date in sql code example

Example 1: date difference in number of days sql server

DECLARE 
    @start_dt DATETIME2= '2019-12-31 23:59:59.9999999', 
    @end_dt DATETIME2= '2020-01-01 00:00:00.0000000';

SELECT 
    DATEDIFF(year, @start_dt, @end_dt) diff_in_year, 
    DATEDIFF(quarter, @start_dt, @end_dt) diff_in_quarter, 
    DATEDIFF(month, @start_dt, @end_dt) diff_in_month, 
    DATEDIFF(dayofyear, @start_dt, @end_dt) diff_in_dayofyear, 
    DATEDIFF(day, @start_dt, @end_dt) diff_in_day, 
    DATEDIFF(week, @start_dt, @end_dt) diff_in_week, 
    DATEDIFF(hour, @start_dt, @end_dt) diff_in_hour, 
    DATEDIFF(minute, @start_dt, @end_dt) diff_in_minute, 
    DATEDIFF(second, @start_dt, @end_dt) diff_in_second, 
    DATEDIFF(millisecond, @start_dt, @end_dt) diff_in_millisecond;

Example 2: SQL server datetime compare

Pressupondo uma tabela utilizador u.

year(u.DataInicio) --> Retorna o ano
month() --> Retorna o mês
day() --> dia

Exemplo:
u.Ativo = 1 AND year(u.DataInicio)<= 2018