我有一个像这样的查询：
SELECT
Mnum, Label , Lvalue ,[Property Type] , RowID, ColumnID, DisplayOrder
FROM
(SELECT
a.Mnum as Mnum, -- 420 fields go here
FROM -- 51 joins go here
) AS MainQuery
UNPIVOT (LabelValue FOR LabelName IN ( --420 fields go here ))
AS UnpvtQuery
INNER JOIN
ReportFieldsLookup rfl on rfl.label = LabelName and rfl.PropType = [PropertyType]
以上显示的查询的细分如下：
上述查询的一部分将在多个表（恰好是51个内部联接）上执行内部联接，并为每个ID吐出420列。我在这个结果表上执行Unpivot操作。这将导致每个ID 420行。
SELECT
Mnum, Label , Lvalue ,[Property Type] , RowID, ColumnID, DisplayOrder
FROM
(SELECT
a.Mnum as Mnum, -- 420 columns go here
FROM -- 51 joins go here
) AS MainQuery
UNPIVOT ( LabelValue FOR LabelName IN ( --420 fields go here ))
结果表将包含以下列：
Mnum varchar
LabelName varchar
Lvalue varchar
PropertyType varchar
示例数据：
8045 Assoc Amenities N/A C/C
8045 Assoc Fees Include n/a C/C
8045 Assoc Pet Rules N/A C/C
8045 Attached/Detached Detached C/C
8045 Avail for Lease No C/C
8045 BRELA No C/C
6012 Assoc Amenities N/A C/C
6012 Assoc Fees Include n/a C/C
6012 Assoc Pet Rules N/A C/C
6012 Attached/Detached Detached C/C
6012 Avail for Lease No C/C
6012 BRELA No C/C
7129 Assoc Amenities AV SFR
7129 Assoc Fees Include yes SFR
7129 Assoc Pet Rules N/A SFR
7129 Change Date N/A SFR
3278 Assoc Amenities Yes lnd
3278 Assoc Fees Include 0 lnd
3278 Assoc Pet Rules N/A lnd
3278 Directions abc lnd
3278 Disclosure aff lnd
当我以24 Mnum's作为输入运行查询的上述部分时，执行查询需要大约6秒。
现在我有另一个表（ReportFieldsLookup），其中包含以下列：
rownum bigint,
Aid varchar
reportid bigint
Label varchar
PropType varchar
DisplayOrder bigint
示例数据：
1 101 1 Assoc Amenities C/C 1
2 101 1 Assoc Fees Include C/C 2
3 101 1 Assoc Pet Rules C/C 3
4 101 1 Avail for Lease C/C 4
5 101 1 Attached/Detached C/C 5
6 101 1 BRELA C/C 6
7 101 1 Assoc Amenities SFR 1
8 101 1 Assoc Fees Include SFR 2
9 101 1 Assoc Pet Rules SFR 3
10 101 1 Change Date SFR 4
11 101 1 Assoc Amenities lnd 1
12 101 1 Assoc Fees Include lnd 2
13 101 1 Assoc Pet Rules lnd 3
14 101 1 Directions lnd 4
15 101 1 Disclosure lnd 5
我试图加入上面显示的两个表格。
INNER JOIN
ReportFieldsLookup rfl ON rfl.label = LabelName AND rfl.PropType = [PropertyType]
结果表：
8045 Assoc Amenities N/A C/C 1
8045 Assoc Fees Include n/a C/C 2
8045 Assoc Pet Rules N/A C/C 3
8045 Attached/Detached Detached C/C 4
8045 Avail for Lease No C/C 5
8045 BRELA No C/C 6
6012 Assoc Amenities N/A C/C 1
6012 Assoc Fees Include n/a C/C 2
6012 Assoc Pet Rules N/A C/C 3
6012 Attached/Detached Detached C/C 4
6012 Avail for Lease No C/C 5
6012 BRELA No C/C 6
7129 Assoc Amenities AV SFR 1
7129 Assoc Fees Include yes SFR 2
7129 Assoc Pet Rules N/A SFR 3
7129 Change Date N/A SFR 4
3278 Assoc Amenities Yes lnd 1
3278 Assoc Fees Include 0 lnd 2
3278 Assoc Pet Rules N/A lnd 3
3278 Directions abc lnd 4
3278 Disclosure aff lnd 5
这需要大约30秒以上。
我该怎么做才能缩短执行时间？
答案 0 :(得分：1)
您可以做的第一件事是确保在被引用的列的所有表中都有索引来进行连接。
假设已经完成并且你需要更多的性能，那就是很多内部联接，所以我在你的代码的MainQuery部分做了一个索引视图： / p>
-- Create a view from the query
CREATE VIEW dbo.MnumIndexedView
WITH SCHEMABINDING
AS
SELECT a.Mnum as Mnum, -- 420 fields go here
FROM -- 51 joins go here
GO
-- Index the view
CREATE UNIQUE CLUSTERED INDEX idx_cl_mnumindexedview
ON dbo.MnumIndexedView(Mnum);
GO
-- Your new query, this time using the indexed view.
SELECT Mnum, Label, Lvalue, [Property Type], RowID, ColumnID, DisplayOrder
FROM dbo.MnumIndexedView WITH (NOEXPAND)
UNPIVOT (LabelValue FOR LabelName IN ( --420 fields go here ))
AS
INNER JOIN ReportFieldsLookup rfl
ON rfl.label = LabelName AND rfl.PropType = [PropertyType]
您不能将整个内容放在索引视图中，因为我认为索引视图不支持PIVOT和UNPIVOT。但是，保留来自众多内部联接的数据应该可以为您带来更好的性能。
请注意，这需要some additional options to be enabled，因为在获取索引视图时，SQL Server可能会有点挑剔。
另请注意在索引视图的查询中使用WITH (NOEXPAND)。在非企业版的SQL Server中，这是必要的，否则优化器将只查询基础表，并且您不会看到任何好处。