SQL hierarchyId上的GetAncestor查詢總是會拉動某些級別

Question

我們通常會被要求在報表中包含特定級別的層次結構，並且我正在尋找一種方法來加快查詢性能並使用hierarchyid。我做了一些測試，並且我有問題，但我認爲性能會更好。以下是針對給定條目抽取2到4級的示例。我想通過GetAncestor（）函數結合hierarchyid的級別來實現這一點。第一個查詢看起來很快，但它被硬編碼爲只返回某一級別的行，以避免使用負值炸燬GetAncestor查詢。第二個樣本解決了這個問題，但速度要慢得多。理想的第二種選擇是我想使用但它不夠快。

--drop table #hier 

CREATE TABLE #hier 
    (
    rec_ID int NOT NULL, 
    rec_NAME varchar(6), 
    nodeID hierarchyid NULL, 
    lvl AS [nodeid].[GetLevel]() PERSISTED 
    ) ON [PRIMARY] 
GO 
ALTER TABLE #hier ADD CONSTRAINT 
    rec_ID PRIMARY KEY CLUSTERED 
    (
    rec_ID 
    ) WITH(STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY] 
GO 
CREATE NONCLUSTERED INDEX IX_hier_nodeID ON #hier 
    (
    nodeID 
    ) WITH(STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY] 
GO 
ALTER TABLE #hier SET (LOCK_ESCALATION = TABLE) 
GO 

insert into #hier (rec_ID, rec_NAME, nodeID) 
    SELECT 1, 'CEO', cast('/' as hierarchyid) 
    union 
    SELECT 2, 'VP1', cast('/1/' as hierarchyid) 
    union 
    SELECT 3, 'VP2', cast('/2/' as hierarchyid) 
    union 
    SELECT 4, 'VP3', cast('/3/' as hierarchyid) 
    union 
    SELECT 5, 'Mgr1', cast('/1/1/' as hierarchyid) 
    union 
    SELECT 6, 'Mgr2', cast('/1/2/' as hierarchyid) 
    union 
    SELECT 7, 'Super1', cast('/1/2/1/' as hierarchyid) 
    union 
    SELECT 8, 'Ldr1', cast('/1/2/1/1/' as hierarchyid) 
    union 
    SELECT 9, 'Work1', cast('/1/2/1/1/1/' as hierarchyid) 
    union 
    SELECT 10, 'Work2', cast('/1/2/1/1/2/' as hierarchyid) 
    union 
    SELECT 11, 'Work3', cast('/1/2/1/1/3/' as hierarchyid) 
GO 

-- this runs fast but is hard coded to a level 

declare @recname varchar(6) 
set @recname = 'Work3' 

select 
    x.rec_name 
    ,x.lvl 
    ,(select rec_name from #hier where nodeid = x.nodeid.GetAncestor(x.lvl - 2)) as l2 
    ,(select rec_name from #hier where nodeid = x.nodeid.GetAncestor(x.lvl - 3)) as l3 
    ,(select rec_name from #hier where nodeid = x.nodeid.GetAncestor(x.lvl - 4)) as l4 
from #hier x 
where x.rec_name = @recname 
    and x.lvl >= 4 


-- this works for all levels but runs too slow 

set @recname = 'Mgr2' 
select 
    x.rec_name 
    ,x.lvl 
    ,case 
     when x.lvl >=2 then (select rec_name from #hier where nodeid = x.nodeid.GetAncestor(x.lvl - 2)) 
     else '*N/A' end as l2 
    ,case 
     when x.lvl >=3 then (select rec_name from #hier where nodeid = x.nodeid.GetAncestor(x.lvl - 3)) 
     else '*N/A' end as l2 
    ,case 
     when x.lvl >=4 then (select rec_name from #hier where nodeid = x.nodeid.GetAncestor(x.lvl - 4)) 
     else '*N/A' end as l2 
from #hier x 
where x.rec_name = @recname 

Answer 1

在我看來，你應該創建以下指標：

1）

CREATE INDEX IX_hier_rec_name_#_lvl_nodeid 
ON #hier (rec_name) 
INCLUDE (lvl, nodeid) 

滿足查詢＃2

select 
    x.rec_name 
    ,x.lvl 
    ,case 
     when x.lvl >=2 then (... = x.nodeid.GetAncestor(x.lvl - 2)) 
     else '*N/A' end as l2 
    ,... 
from #hier x 
where x.rec_name = @recname 

注：查詢＃1你可以使用

CREATE INDEX IX_hier_rec_name_lvl_#_nodeid 
ON #hier (rec_name, lvl) 
INCLUDE (nodeid) 

和

2）你應該

CREATE INDEX IX_hier_nodeID_#_rec_name 
ON #hier (nodeid) 
INCLUDE (rec_name) 

或（更好）與

CREATE UNIQUE INDEX IUN_hier_nodeID_#_rec_name 
ON #hier (nodeid) 
INCLUDE (rec_name) 

如果nodeid值改變這一指數IX_hier_nodeID不允許重複。