对于Nvarchar（Max），我只能在TSQL中获得4000个字符？

这是SS 2005的。

为什么我只有4000个字符而不是8000个字符？

它在4000处截断string@SQL1。

ALTER PROCEDURE sp_AlloctionReport( @where NVARCHAR(1000), @alldate NVARCHAR(200), @alldateprevweek NVARCHAR(200)) AS DECLARE @SQL1 NVARCHAR(Max) SET @SQL1 = 'SELECT DISTINCT VenueInfo.VenueID, VenueInfo.VenueName, VenuePanels.PanelID, VenueInfo.CompanyName, VenuePanels.ProductCode, VenuePanels.MF, VenueInfo.Address1, VenueInfo.Address2, '' As AllocationDate, '' As AbbreviationCode, VenueInfo.Suburb, VenueInfo.Route, VenueInfo.ContactFirstName, VenueInfo.ContactLastName, VenueInfo.SuitableTime, VenueInfo.OldVenueName, VenueCategories.Category, VenueInfo.Phone, VenuePanels.Location, VenuePanels.Comment, [VenueCategories].[Category] + '' Allocations'' AS ReportHeader, ljs.AbbreviationCode AS PrevWeekCampaign FROM (((VenueInfo INNER JOIN VenuePanels ON VenueInfo.VenueID = VenuePanels.VenueID) INNER JOIN VenueCategories ON VenueInfo.CategoryID = VenueCategories.CategoryID) LEFT JOIN (SELECT CampaignProductions.AbbreviationCode, VenuePanels.PanelID, CampaignAllocations.AllocationDate FROM (((VenueInfo INNER JOIN VenuePanels ON VenueInfo.VenueID=VenuePanels.VenueID) INNER JOIN CampaignAllocations ON VenuePanels.PanelID=CampaignAllocations.PanelID) INNER JOIN CampaignProductions ON CampaignAllocations.CampaignID=CampaignProductions.CampaignID) INNER JOIN VenueCategories ON VenueInfo.CategoryID=VenueCategories.CategoryID WHERE ' + @alldateprevweek + ') ljs ON VenuePanels.PanelID = ljs.PanelID) INNER JOIN (SELECT VenueInfo.VenueID, VenuePanels.PanelID, VenueInfo.VenueName, VenueInfo.CompanyName, VenuePanels.ProductCode, VenuePanels.MF, VenueInfo.Address1, VenueInfo.Address2, CampaignAllocations.AllocationDate, CampaignProductions.AbbreviationCode, VenueInfo.Suburb, VenueInfo.Route, VenueInfo.ContactFirstName, VenueInfo.ContactLastName, VenueInfo.SuitableTime, VenueInfo.OldVenueName, VenueCategories.Category, VenueInfo.Phone, VenuePanels.Location, VenuePanels.Comment, [Category] + '' Allocations'' AS ReportHeader, ljs2.AbbreviationCode AS PrevWeekCampaign FROM ((((VenueInfo INNER JOIN VenuePanels ON VenueInfo.VenueID = VenuePanels.VenueID) INNER JOIN CampaignAllocations ON VenuePanels.PanelID = CampaignAllocations.PanelID) INNER JOIN CampaignProductions ON CampaignAllocations.CampaignID = CampaignProductions.CampaignID) INNER JOIN VenueCategories ON VenueInfo.CategoryID = VenueCategories.CategoryID) LEFT JOIN (SELECT CampaignProductions.AbbreviationCode, VenuePanels.PanelID, CampaignAllocations.AllocationDate FROM (((VenueInfo INNER JOIN VenuePanels ON VenueInfo.VenueID=VenuePanels.VenueID) INNER JOIN CampaignAllocations ON VenuePanels.PanelID=CampaignAllocations.PanelID) INNER JOIN CampaignProductions ON CampaignAllocations.CampaignID=CampaignProductions.CampaignID) INNER JOIN VenueCategories ON VenueInfo.CategoryID=VenueCategories.CategoryID WHERE ' + @alldateprevweek + ') ljs2 ON VenuePanels.PanelID = ljs2.PanelID WHERE ' + @alldate + ' AND ' + @where + ') ljs3 ON VenueInfo.VenueID = ljs3.VenueID WHERE (((VenuePanels.PanelID)<>ljs3.[PanelID] And (VenuePanels.PanelID) Not In (SELECT PanelID FROM CampaignAllocations WHERE ' + @alldateprevweek + ')) AND ' + @where + ') UNION ALL SELECT VenueInfo.VenueID, VenueInfo.VenueName, VenuePanels.PanelID, VenueInfo.CompanyName, VenuePanels.ProductCode, VenuePanels.MF, VenueInfo.Address1, VenueInfo.Address2, CampaignAllocations.AllocationDate, CampaignProductions.AbbreviationCode, VenueInfo.Suburb, VenueInfo.Route, VenueInfo.ContactFirstName, VenueInfo.ContactLastName, VenueInfo.SuitableTime, VenueInfo.OldVenueName, VenueCategories.Category, VenueInfo.Phone, VenuePanels.Location, VenuePanels.Comment, [Category] + '' Allocations'' AS ReportHeader, ljs.AbbreviationCode AS PrevWeekCampaign FROM ((((VenueInfo INNER JOIN VenuePanels ON VenueInfo.VenueID = VenuePanels.VenueID) INNER JOIN CampaignAllocations ON VenuePanels.PanelID = CampaignAllocations.PanelID) INNER JOIN CampaignProductions ON CampaignAllocations.CampaignID = CampaignProductions.CampaignID) INNER JOIN VenueCategories ON VenueInfo.CategoryID = VenueCategories.CategoryID) LEFT JOIN (SELECT CampaignProductions.AbbreviationCode, VenuePanels.PanelID, CampaignAllocations.AllocationDate FROM (((VenueInfo INNER JOIN VenuePanels ON VenueInfo.VenueID=VenuePanels.VenueID) INNER JOIN CampaignAllocations ON VenuePanels.PanelID=CampaignAllocations.PanelID) INNER JOIN CampaignProductions ON CampaignAllocations.CampaignID=CampaignProductions.CampaignID) INNER JOIN VenueCategories ON VenueInfo.CategoryID=VenueCategories.CategoryID WHERE ' + @alldateprevweek + ') ljs ON VenuePanels.PanelID = ljs.PanelID WHERE ' + @alldate + ' AND ' + @where Select @SQL1 

Answer 1

你已经声明这个nvarchar（max），它允许2GB的数据，所以它将存储2GB。

发生什么事：

• 在分配给@ sql1之前，数据types还不是nvarchar（max）
• 在此之前，它是一个string的集合，每个stringless于4000（ 常量 ）
• 您将短常量与短variables连接（short = <4000）
• 所以你有4000个字符放入@ sql1

所以，你必须确保右边有nvarchar（max）。

一个想法。 第二行连接nvarchar（max）和一个常量= nvarchar（max）

 SET @SQL1 = '' SET @SQL1 = @SQL1 + 'SELECT DISTINCT Venue... .... 

这与每个语言中发生的整数除法没有什么不同。

 declare @myvar float set @myvar = 1/2 --gives zero because it's integer on the right 

运算符优先级（推断数据types优先级）始终是“分配”最后…为什么要在SQL Server中的unicodestring有什么不同？

Answer 2

更新 ： gbn的评论是正确的，我错了。 正如MSDN指出的那样，nvarchar（max）最多支持2 ^ 31-1个字节的数据，以UCS-2（每个字符2个字节，外加2个BOM）存储。 你的问题似乎是string连接，而不是数据types限制。

这就是说，如果你使用它来构build一个SQLstring，为什么不使用VARCHAR？ 你有没有数据库的本地字符集（通常拉丁-1）不可表示的字段名称？

最后 – 通过在存储过程中不使用dynamicSQL，可以简化整个问题。 创build一些带有where子句string和返回表的表值函数，然后在您的过程中join它们。 作为奖励，它几乎肯定会快得多，因为至less数据库将能够将SP主体caching为准备好的语句。

Answer 3

我解决问题只是在每个string之前包含N个字符，例如解决问题

 declare @sql nvarchar(max) = '' + @Where + 'SomeThing'; 

一定是

 declare @sql nvarchar(max) = N'' + @Where + N'SomeThing'; 

如果你设置string为空还必须设置N“

 if @where is null set @where = N'' 

:-)简单的答案