>我使用此存储过程显示文档处于挂起状态
create procedure b
as
select
dbo.DocumentInfo.DocID, dbo.DocumentInfo.DocName,
dbo.DocumentInfo.Uploadfile, dbo.DocType.Doc Type,
dbo.Department.DepType, ApproveType.ApproveType
from
dbo.DocumentInfo
left join
dbo.DocType on dbo.DocumentInfo.DocTypeID = dbo.DocType.DocTypeID
left join
dbo.Department on dbo.DocumentInfo.DepID = dbo.Department.DepID
inner join
ApproveType on DocumentInfo.ApproveID = ApproveType.ApproveID
and (ApproveType.ApproveID = 3)
但是当我检查此查询时,它无法向我显示任何文档。
问题出在哪里?
您的问题是您在联接排除数据的表上直接联接(内部联接)。 因此,要么表 DocumentInfo
中的列ApproveID
不包含任何数据,要么表 ApproveType
中没有匹配的行用于列ApproveID
。
以这种方式使用此存储过程,则在任何情况下都不正确地使用了连接 - 并且您绝对可以考虑使用表别名,如下所示:
CREATE PROCEDURE b
AS
SELECT di.DocID,
di.DocName,
di.Uploadfile,
dt.DocType,
d.DepType,
at.ApproveType
FROM DocumentInfo di
LEFT OUTER JOIN
DocType dt ON dt.DocTypeID = di.DocTypeID
LEFT OUTER JOIN
Department d ON d.DepID = di.DepID
LEFT OUTER JOIN
ApproveType at ON at.ApproveID = di.ApproveID
AND at.ApproveID = 3