Add second

How to add second to date DATEADD function with getdate, sysdatetime, current_timestamp.

Examples

select dateadd(S, 2, '2018-01-06 18:01:10.777');

select dateadd(SS, 3, '2018-01-06 18:01:10.777');

select dateadd(SECOND, 4, '2018-01-06 18:01:10.777');

select dateadd(SECOND, 1, getdate());

select dateadd(SECOND, 2, sysdatetime());

select dateadd(SECOND, 3, current_timestamp);