Check for leap year

MOST EFFICIENT LEAP YEAR TEST:

CASE WHEN @YEAR & 3 = 0 AND (@YEAR % 25 <> 0 OR @YEAR & 15 = 0) THEN ...

Adapted from: http://stackoverflow.com/a/11595914/3466415

Leap year calculation:

(@year % 4 = 0) and (@year % 100 != 0) or (@year % 400 = 0)

When this is true, then it is a leap year. Or to put it in case statement

select case when
    (
        (@year % 4 = 0) and (@year % 100 != 0) or
        (@year % 400 = 0)
    ) then 'LEAP' else 'USUAL' end
;

Check for 29th Feb:

CASE WHEN ISDATE(CAST(@YEAR AS char(4)) + '0229') = 1 THEN 'LEAP YEAR' ELSE 'NORMAL YEAR' END

or use the following rule

CASE WHEN (@YEAR % 4 = 0 AND @YEAR % 100 <> 0) OR @YEAR % 400 = 0 THEN 'LEAP YEAR'...

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