的毗連結果在一個字符串中的存儲過程

Question

在我的存儲過程返回空值，我串聯我的結果到像一個字符串：

Problem1|Problem2|Problem3 

當我試圖在一個變量@display來存儲，它將返回null 。當我運行查詢而不將其存儲到變量時，它會返回結果。不知道爲什麼它返回null？

declare @display nvarchar(500) 

select 
@display = @display + gp2.ProblemDesc + '|' 
from (SELECT gp.GrantProblemID, gp.ProblemDesc, gps.GrantProblemStatus, row_number() over (partition by gp.grantproblemid order by p.periodid desc) ranking from MergedProgressReport.dbo.[PeriodAgencyGrantProblems] pagp 
inner join MergedProgressReport.dbo.PeriodAgencyGrants pag on pag.PeriodAgencyGrantsID = pagp.PeriodAgencyGrantID and pag.GrantNumber = '2011UMWX0001' 
inner join MergedProgressReport.dbo.periodagencyinfo pai on pag.PeriodAgencyInfoID = pai.PeriodAgencyInfoID inner join MergedProgressReport.dbo.Periods p on p.PeriodID = pai.PeriodID 
inner join MergedProgressReport.dbo.GrantProblemStatus gps on pagp.GrantProblemStatusID = gps.GrantProblemStatusID inner join MergedProgressReport.dbo.GrantProblems gp on pagp.GrantProblemID = gp.GrantProblemID and gp.GrantProblemAreaID = 7) xx 
right join MergedProgressReport.dbo.GrantProblems gp2 on xx.GrantProblemID = gp2.GrantProblemID and xx.ranking = 1 where gp2.GrantProblemAreaID = 7 

Select @display 

Answer 1

試試這個。可能你需要初始化變量。

declare @display nvarchar(500) 
set @display = '' 

總之，在聲明變量之後編寫查詢之前，您已經缺少set語句。