CASE
isn't used for flow control... for this, you would need to use IF
...
But, there's a set-based solution to this problem instead of the procedural approach:
UPDATE tblEmployee
SET
InOffice = CASE WHEN @NewStatus = 'InOffice' THEN -1 ELSE InOffice END,
OutOffice = CASE WHEN @NewStatus = 'OutOffice' THEN -1 ELSE OutOffice END,
Home = CASE WHEN @NewStatus = 'Home' THEN -1 ELSE Home END
WHERE EmpID = @EmpID
Note that the ELSE
will preserves the original value if the @NewStatus
condition isn't met.