Question

我是SQL的初学者，我正在尝试运行以下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

上述目的是获取所有行@Status is NULL，并过滤行，如果参数已分配给@Status。 @Category（varchar）和@Status（int）是IN paramateres

当@Status为NULL时，这可以正常工作，即我得到所有记录。但是如果我传递一个参数，比如@Status = 2，即使有一些记录可用，执行也不会返回任何行。

首先，我如何得到我想要的结果？其次，如果没有if条件块，有没有更好的方法呢？

Answer 1

实际上，你的结果是

select * from something where ps.Category ='some string, containing and ps.Status= inside'

因此预期结果为空行集你想要这样的东西（希望状态是数字，而不是字符串）

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)

好的，这里是不信任的测试： - ）

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

您可以通过以下方式简单地设置条件以获得所需的结果

--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

由于

将参数添加到where子句sql

2 个答案: