SQL CASE表达式返回集null和not null

Question

我有任务，其需要一个参数，并具有结果

例 参数名称是sizePram（1三种模式=只有零，2 =只不空，3 =二者或全部）

declare @sizeParam int 
set @sizeParam = 1 or 2 or 3 

select * from SalesLT.Product where Size = 
CASE @sizeParam 
    when 1 then is null 
    when 2 then is not null 
    when 3 then all 
end 

Answer 1

select * 
from SalesLT.Product 
where 
    (@sizeParam = 1 and Size is null) or 
    (@sizeParam = 2 and Size is not null) or 
    (@sizeParam = 3) 

Answer 2

SELECT * 
    FROM SalesLT.Product 
    WHERE (@sizeParam = 1 AND Size IS NULL) 
     OR (@sizeParam = 2 AND Size IS NOT NULL) 
     OR (@sizeParam = 3) 

Answer 3

SELECT * 
    FROM SalesLT.Product 
WHERE (sizeParam <> 1 OR Size IS NULL) 
     AND NOT (sizeParam = 2 AND Size IS NULL);