Adding parameters to where clause sql - sql-server-2012

Question

I am something of a beginner to SQL and I am trying to run the following SP.
DECLARE #stringStatus varchar(100)
--Check for status value
IF #Status is NULL
BEGIN
set #stringStatus = ''
END
ELSE
BEGIN
set #stringStatus = ' and ps.Status = ' + CAST(#Status as varchar)
END
select * from Projects p
join projectstatus ps on p.pid = ps.pid
where ps.Category = isnull(#Category, p.Category) + #stringStatus
The aim of the above is to get all rows if #Status is NULL, and to filter the rows, if a parameter has been assigned to #Status.
#Category (varchar) and #Status (int) are IN paramateres
This works fine when #Status is NULL, i.e, I get all the records. But if I pass a parameter, say, #Status = 2, the execution returns no rows, even though there are a few records available.
First of all, how do I get my desired results? Secondly, is there a better way to do this without an if condition block?

Answer 1

Actually, your result is
select * from something where ps.Category ='some string, containing and ps.Status= inside'
So empty rowset is expected result.
You want something like this (hope status is number, not string)
select * from Projects p
join projectstatus ps on p.pid = ps.pid
where ps.Category = isnull(#Category, p.Category) and
(#Status is NULL OR ps.Status = #Status)
Ok, here are tests for mistrustful :-)
declare #projects table
(
pid int,
name nvarchar(20),
category int
);
declare #projectstatus table
(
pid int,
Category int,
status int
);
insert into #projects values
(1,'Project 1', 1),(2,'Project 2',1),(3,'Project 3',1),(4,'Project 4',1),(5,'Project 5',1);
insert into #projectstatus values
(1,1,1),(2,1,2),(3,1,3),(4,1,2),(5,1,NULL);
declare #Category int =null;
declare #Status int;
--first of all, do not understand, what is the logic with category
--category in one table should be the same, than in other table or specified?
--ok, you said with category everything is ok, do not test category, test status
--test with null
set #Status=null
select * from #Projects p
join #projectstatus ps on p.pid = ps.pid
where ps.Category = isnull(#Category, p.Category) and
(#Status is NULL OR ps.Status = #Status)
--test with existing status
set #Status=1
select * from #Projects p
join #projectstatus ps on p.pid = ps.pid
where ps.Category = isnull(#Category, p.Category) and
(#Status is NULL OR ps.Status = #Status)
--test with not existing status
set #Status=10
select * from #Projects p
join #projectstatus ps on p.pid = ps.pid
where ps.Category = isnull(#Category, p.Category) and
(#Status is NULL OR ps.Status = #Status)

Answer 2

You can simple put condition in the below way for your desired results
--Check for status value
IF #Status is NULL
BEGIN
select * from Projects p
join projectstatus ps on p.pid = ps.pid
where ps.Category = isnull(#Category, p.Category)
END
ELSE
BEGIN
select * from Projects p
join projectstatus ps on p.pid = ps.pid
where ps.Category = isnull(#Category, p.Category) + #stringStatus
END
Thanks