需要一些关于自加入问题的认真帮助

https://stackoverflow.com/questions/3046058

27-09-2019
|

题

正如您可能知道的，您无法通过自连接对视图进行索引。实际上，甚至同一个表的两个连接，即使它在技术上不是自连接。微软的几个人想出了一个解决办法。但是太复杂了，看不懂！！！

问题的解决方案在这里： http://jmkehayias.blogspot.com/2008/12/creating-indexed-view-with-self-join.html

我想要应用此工作的视图是：

create VIEW vw_lookup_test
WITH SCHEMABINDING
AS
select
count_big(*) as [count_all],
awc_txt,
city_nm,
str_nm,
stru_no,
o.circt_cstdn_nm [owner],
t.circt_cstdn_nm [tech],
dvc.circt_nm,
data_orgtn_yr 
from 
((dbo.dvc 
join dbo.circt 
on dvc.circt_nm = circt.circt_nm) 
join dbo.circt_cstdn o
on circt.circt_cstdn_user_id = o.circt_cstdn_user_id)
join dbo.circt_cstdn t
on dvc.circt_cstdn_user_id = t.circt_cstdn_user_id
group by
awc_txt,
city_nm,
str_nm,
stru_no,
o.circt_cstdn_nm,
t.circt_cstdn_nm,
dvc.circt_nm,
data_orgtn_yr 
go

任何帮助将不胜感激！

非常感谢！

编辑：所以我发现这也行得通。请注意，我在第一个索引视图中加入表一次，并在第二个非索引视图中加入第二次。

alter VIEW vw_lookup_owner_test2
WITH SCHEMABINDING  
AS 
select
count_big(*) as [countAll],
awc_txt,
city_nm,
str_nm,
stru_no,
dvc.circt_nm,
circt_cstdn_nm,
data_orgtn_yr,
dvc.circt_cstdn_user_id
from dbo.dvc 
join dbo.circt
on dvc.circt_nm = circt.circt_nm
join dbo.circt_cstdn o
on circt.circt_cstdn_user_id = o.circt_cstdn_user_id
group by
awc_txt,
city_nm,
str_nm,
stru_no,
dvc.circt_nm,
circt_cstdn_nm,
data_orgtn_yr,
dvc.circt_cstdn_user_id
go

和

CREATE UNIQUE CLUSTERED INDEX [idx_vw_lookup_owner2_test1] ON [dbo].[vw_lookup_owner_test2] 
(
    [awc_txt] ASC,
    [city_nm] ASC,
    [str_nm] ASC,
    [stru_no] ASC,
    [circt_nm] ASC,
    [circt_cstdn_nm] ASC,
    [data_orgtn_yr] ASC,
    [circt_cstdn_user_id] ASC
)WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, SORT_IN_TEMPDB = OFF, IGNORE_DUP_KEY = OFF, DROP_EXISTING = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]
GO

和

create view vw_lookup_dvc_loc
as
select
awc_txt,
city_nm,
str_nm,
stru_no,
circt_nm,
o.circt_cstdn_nm as [owner],
--o.circt_cstdn_user_id,
t.circt_cstdn_nm as tech,
data_orgtn_yr
from vw_lookup_owner_test2 o With (NOEXPAND)
join circt_cstdn t
on o.circt_cstdn_user_id = t.circt_cstdn_user_id
group by
awc_txt,
city_nm,
str_nm,
stru_no,
circt_nm,
o.circt_cstdn_nm,
data_orgtn_yr,
t.circt_cstdn_nm
--o.circt_cstdn_user_id

然后我可以根据需要在第一个视图上创建附加索引。我不确定这个解决方案（或解决该问题的方法）是否真的会加快性能，但我会让您知道。

解决方案

这是我从博客文章中得到的内容

假设您想在 dbo.circt_cstdn 上加入 2 次，即你想要类似的东西
```
         owner       tech
rowA     a.nm        b.nm
...
```
不是将值放入 2 列，而是将其放入 2 行（上面每行 2 行），并添加一个附加列来说明哪一行对应哪一列。请注意，第 1.1 行和第 1.2 行具有相同的数据（名称和列除外）
```
         name   for
row1.1   nm     owner
row1.2   nm     tech
...
```
然后，您以所有者和技术人员的名称列的最大值为中心。注意 - 最大函数只是为了欺骗枢轴（需要一些汇总函数），如果只有一个记录所有者Tech Row1 NM NM NM NM ...

现在，如果我们为您的查询执行此操作

创建一个表d，像这样
```
 i
 1
 2
```

与此交叉连接查询的第一部分

SELECT 
     count_big(*) as [count_all], 
     awc_txt, 
     city_nm, 
     str_nm, 
     stru_no, 
     dvc.circt_nm, 
     data_orgtn_yr
FROM  
     dbo.dvc  
     INNER JOIN dbo.circt on dvc.circt_nm = circt.circt_nm
     CROSS JOIN dbo.d  
GROUP BY
     awc_txt, city_nm, str_nm, stru_no, dvc.circt_nm, data_orgtn_yr, d.i

现在，如果 D.i 为 1，则使用所有者行；如果 D.i 为 2，则使用技术

SELECT 
     count_big(*) as [count_all], 
     awc_txt, 
     city_nm, 
     str_nm, 
     stru_no, 
     dvc.circt_nm, 
     data_orgtn_yr,
     Case 
         WHEN d.i = 1 THEN 'Owner'
         WHEN d.i = 2 THEN 'Tech'
     END
FROM  
     dbo.dvc  
     INNER JOIN dbo.circt on dvc.circt_nm = circt.circt_nm
     CROSS JOIN dbo.d 
GROUP BY
     awc_txt, city_nm, str_nm, stru_no, dvc.circt_nm, data_orgtn_yr, 
     Case 
         WHEN d.i = 1 THEN 'Owner'
         WHEN d.i = 2 THEN 'Tech'
     END

现在添加 nm 列。要获取名称，如果它是所有者行 (d.i = 1)，请使用 circt 加入 circt_cstdn；如果它是技术行 (d.i = 2)，请加入 dvc。注意 - 我在这里尝试了一种快捷方式，将其放入连接条件中。如果它不起作用，请尝试博客文章方式（在 circt.circt_cstdn_user_id 上进行连接或者 dvc.circt_cstdn_user_id，然后使用WHERE子句过滤掉）

SELECT 
     count_big(*) as [count_all], 
     awc_txt, 
     city_nm, 
     str_nm, 
     stru_no, 
     dvc.circt_nm, 
     data_orgtn_yr,
     Case 
         WHEN d.i = 1 THEN 'Owner'
         WHEN d.i = 2 THEN 'Tech'
     END as PersonType,
     circt_cstdn_nm
FROM  
     dbo.dvc  
     INNER JOIN dbo.circt on dvc.circt_nm = circt.circt_nm
     CROSS JOIN dbo.d 
     INNER JOIN dbo.circt_cstdn on circt_cstdn_user_id = 
          CASE
               WHEN d.i = 1 THEN circt.circt_cstdn_user_id
               WHEN d.i = 2 THEN dvc.circt_cstdn_user_id
          END
GROUP BY
     awc_txt, city_nm, str_nm, stru_no, dvc.circt_nm, data_orgtn_yr, 
     Case 
         WHEN d.i = 1 THEN 'Owner'
         WHEN d.i = 2 THEN 'Tech'
     END,
     circt_cstdn_nm

使用它创建一个视图并创建索引

create VIEW vw_lookup_test_imed
WITH SCHEMABINDING 
AS
    <<query above>>  
GO

spell to create INDEX

现在，您可以通过 PIVOT 将 PersonType 列转换为 Owner 和 Tech 列

SELECT 
     count_all, 
     awc_txt, 
     city_nm, 
     str_nm, 
     stru_no, 
     dvc.circt_nm, 
     data_orgtn_yr,
     [Owner], 
     [Tech] 
FROM 
( 
     SELECT 
          count_all, 
          awc_txt, 
          city_nm, 
          str_nm, 
          stru_no, 
          dvc.circt_nm, 
          data_orgtn_yr,
          PersonType,
          circt_cstdn_nm
     FROM dbo.vw_lookup_test_imed WITH (NOEXPAND) 
) src 
PIVOT 
( 
     MAX(circt_cstdn_nm) 
     FOR PersonType IN ([Owner], [Tech]) 
) pvt

如果存在语法错误（肯定有很多错误，因为我现在无法访问数据库），请告诉我。

其他提示

我认为这JOIN语法是可怕的和源自MS访问。啊。我建议你使用：

select
count_big(*) as [count_all],
awc_txt,
city_nm,
str_nm,
stru_no,
o.circt_cstdn_nm [owner],
t.circt_cstdn_nm [tech],
dvc.circt_nm,
data_orgtn_yr 

-- HERE
from dbo.dvc
join dbo.circt on (dvc.circt_nm = circt.circt_nm) 
join dbo.circt_cstdn o on (circt.circt_cstdn_user_id = o.circt_cstdn_user_id)
join dbo.circt_cstdn t on (dvc.circt_cstdn_user_id = t.circt_cstdn_user_id)

group by
awc_txt,
city_nm,
str_nm,
stru_no,
o.circt_cstdn_nm,
t.circt_cstdn_nm,
dvc.circt_nm,
data_orgtn_yr

这句法更干净，更容易理解和SQL Server，火鸟，甲骨文，MySQL和其他多是公认的。现在你可以看到更好的“表”之间的关系。当您加入相同的“表”两次或更多次，你需要别名每一个。在一行“circt_cstdn”的别名是“O”。上的其他线， “circt_cstdn” 的别名为 “T”。

我建议使用LEFT的JOIN或INNER JOIN代替JOIN。

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