具有CASE / WHEN和NULL值的SQL Server 2008 WHERE子句

Question

I'm trying to write something like :

SELECT *
FROM MyTable m
WHERE m.Category = CASE WHEN @Category IS NULL THEN m.Category ELSE @Category END

Basically, I need lines where m.Category equals @Category if this one has a value ; else, I need all lines.

BUT if m.Category has NULL value, the line is NOT send back because SQL needs something lile WHERE m.Category IS NULL and not WHERE m.Category = NULL .

So, how could I modify my request to tell to SQL : "I need ALL lines if @Category is null (even lines where m.Category is null), but if @Category has a value, I just need lines where m.Category matches @Category ?

Answer 1

you can write it like this:

select *
from MyTable m
where @Category is null or m.Category = @Category