从字符串转换为uniqueidentifier时转换失败

这失败了：

 DECLARE @vPortalUID NVARCHAr(32) SET @vPortalUID='2A66057D-F4E5-4E2B-B2F1-38C51A96D385' DECLARE @nPortalUID AS UNIQUEIDENTIFIER SET @nPortalUID = CAST(@vPortalUID AS uniqueidentifier) PRINT @nPortalUID

这有效

 DECLARE @vPortalUID NVARCHAr(36) SET @vPortalUID='2A66057D-F4E5-4E2B-B2F1-38C51A96D385' DECLARE @nPortalUID AS UNIQUEIDENTIFIER SET @nPortalUID = CAST(@vPortalUID AS UNIQUEIDENTIFIER) PRINT @nPortalUID

所不同的是

NVARCHAr(36)