7
當怪怪的我有一個串接查詢:VARCHAR(MAX)串聯串
DECLARE @path NVARCHAR(max)
SELECT @path = ISNULL(@path + '/', '') + url_segment
FROM navigation_self_and_parents(2813) ORDER BY depth ASC
SELECT @path
navigation_self_and_parents(2813)
回報
id par_id title url_segment sequence depth 2813 2816 testing1234 testing1234 0 0 2816 2809 U /fixedurl 0 -1 2809 NULL E E 0 -2
我串接查詢返回
'testing1234' when using `NVARCHAR(MAX)` and 'E//fixedurl/testing1234' when using `NVARCHAR(4000)`
我最好的猜測是使用NVARCHAR(MAX)
會導致@path在每次設置時都會被重新輸入,因此在重新輸入之前丟失了內容集,或者在第一次設置時輸入了內容,然後後續的連接調用將自動失敗。
我很想真正理解這種行爲的根本原因。
UPDATE
navigation_self_and_parents:
USE [SomeDatabase]
GO
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
ALTER FUNCTION [dbo].[navigation_self_and_parents]
(
@id int
)
RETURNS TABLE
AS
RETURN
(
WITH navigation_self_and_parents (id, parent_id, title, url_segment, sequence_number, depth)
AS
(
SELECT id, parent_id, title, url_segment, sequence_number, 0 FROM navigation_node WHERE [email protected]
UNION ALL
SELECT n.id, n.parent_id, n.title, n.url_segment, n.sequence_number, depth - 1 From navigation_node as n
INNER JOIN navigation_self_and_parents as rn
ON n.id = rn.parent_id
)
SELECT * FROM navigation_self_and_parents
)
navigation_node DDL:
CREATE TABLE [dbo].[navigation_node](
[id] [int] IDENTITY(1,1) NOT NULL,
[title] [nvarchar](128) NULL,
[url_segment] [nvarchar](max) NULL,
[hidden] [bit] NOT NULL,
[page_id] [int] NULL,
[parent_id] [int] NULL,
[sequence_number] [int] NOT NULL,
[createdOn] [datetime] NOT NULL,
[updatedOn] [datetime] NULL,
[navigation_type_id] [int] NULL,
...snap
'url_segment`類型是什麼? – 2011-01-24 10:02:29
我以前使用這種方法進行連接時有類似的結果。 (它只以一行的值而不是全部結束)我從未注意到`datatype`已經起作用了。有時您需要稍微調整一下查詢以獲取所需的執行計劃。你可以發佈兩個計劃嗎? (或者你當然可以像使用XML PATH一樣在SQL Server 2005上進行文檔編寫工作)參見http://support.microsoft.com/kb/287515/en-us – 2011-01-24 10:11:08