适用于 Microsoft SQL Server 2008 R2。
问题是
如果我们有几十个 Outer Apply
(30),那么它们开始工作的速度会很慢。在 Outer Apply
中间,我有一些比简单选择更复杂的东西,一个 View 。
详情
我正在编写一种分配给表(在数据库中)的属性。通常,几个表,保存对表的属性(键,值)的引用。
伪结构如下所示:
DECLARE @Lot TABLE (
LotId INT PRIMARY KEY IDENTITY,
SomeText VARCHAR(8))
INSERT INTO @Lot
OUTPUT INSERTED.*
VALUES ('Hello'), ('World')
DECLARE @Attribute TABLE(
AttributeId INT PRIMARY KEY IDENTITY,
LotId INT,
Val VARCHAR(8),
Kind VARCHAR(8))
INSERT INTO @Attribute
OUTPUT INSERTED.* VALUES
(1, 'Foo1', 'Kind1'), (1, 'Foo2', 'Kind2'),
(2, 'Bar1', 'Kind1'), (2, 'Bar2', 'Kind2'), (2, 'Bar3', 'Kind3')
LotId SomeText
----------- --------
1 Hello
2 World
AttributeId LotId Val Kind
----------- ----------- -------- --------
1 1 Foo1 Kind1
2 1 Foo2 Kind2
3 2 Bar1 Kind1
4 2 Bar2 Kind2
5 2 Bar3 Kind3
我现在可以运行如下查询:
SELECT
[l].[LotId]
, [SomeText]
, [Oa1].[AttributeId]
, [Oa1].[LotId]
, 'Kind1Val' = [Oa1].[Val]
, [Oa1].[Kind]
, [Oa2].[AttributeId]
, [Oa2].[LotId]
, 'Kind2Val' = [Oa2].[Val]
, [Oa2].[Kind]
, [Oa3].[AttributeId]
, [Oa3].[LotId]
, 'Kind3Val' = [Oa3].[Val]
, [Oa3].[Kind]
FROM @Lot AS l
OUTER APPLY(SELECT * FROM @Attribute AS la WHERE la.[LotId] = l.[LotId] AND la.[Kind] = 'Kind1') AS Oa1
OUTER APPLY(SELECT * FROM @Attribute AS la WHERE la.[LotId] = l.[LotId] AND la.[Kind] = 'Kind2') AS Oa2
OUTER APPLY(SELECT * FROM @Attribute AS la WHERE la.[LotId] = l.[LotId] AND la.[Kind] = 'Kind3') AS Oa3
LotId SomeText AttributeId LotId Kind1Val Kind AttributeId LotId Kind2Val Kind AttributeId LotId Kind3Val Kind
----------- -------- ----------- ----------- -------- -------- ----------- ----------- -------- -------- ----------- ----------- -------- --------
1 Hello 1 1 Foo1 Kind1 2 1 Foo2 Kind2 NULL NULL NULL NULL
2 World 3 2 Bar1 Kind1 4 2 Bar2 Kind2 5 2 Bar3 Kind3
获取属性值透视表的简单方法和没有属性的 Lot 行的结果,如 Kind3。 我知道微软PIVOT它并不简单,不适合放在这里。
最后,什么会更快并且会产生相同的结果?
最佳答案
为了获得结果,您可以反透视 然后透视 数据。
您可以通过两种方式执行此操作。首先,您可以使用 UNPIVOT
和 PIVOT
函数:
select *
from
(
select LotId,
SomeText,
col+'_'+CAST(rn as varchar(10)) col,
value
from
(
select l.LotId,
l.SomeText,
cast(a.AttributeId as varchar(8)) attributeid,
cast(a.LotId as varchar(8)) a_LotId,
a.Val,
a.Kind,
ROW_NUMBER() over(partition by l.lotid order by a.attributeid) rn
from @Lot l
left join @Attribute a
on l.LotId = a.LotId
) src
unpivot
(
value
for col in (attributeid, a_Lotid, val, kind)
) unpiv
) d
pivot
(
max(value)
for col in (attributeid_1, a_LotId_1, Val_1, Kind_1,
attributeid_2, a_LotId_2, Val_2, Kind_2,
attributeid_3, a_LotId_3, Val_3, Kind_3)
) piv
参见 SQL Fiddle with Demo .
或者从 SQL Server 2008+ 开始,您可以使用带有 VALUES
子句的CROSS APPLY
来逆透视数据:
select *
from
(
select LotId,
SomeText,
col+'_'+CAST(rn as varchar(10)) col,
value
from
(
select l.LotId,
l.SomeText,
cast(a.AttributeId as varchar(8)) attributeid,
cast(a.LotId as varchar(8)) a_LotId,
a.Val,
a.Kind,
ROW_NUMBER() over(partition by l.lotid order by a.attributeid) rn
from @Lot l
left join @Attribute a
on l.LotId = a.LotId
) src
cross apply
(
values ('attributeid', attributeid),('LotId', a_LotId), ('Value', Val), ('Kind', Kind)
) c (col, value)
) d
pivot
(
max(value)
for col in (attributeid_1, LotId_1, Value_1, Kind_1,
attributeid_2, LotId_2, Value_2, Kind_2,
attributeid_3, LotId_3, Value_3, Kind_3)
) piv
参见 SQL Fiddle with Demo .
unpivot 过程为每个 LotID
和 SomeText
获取多个列,并将其转换为行,给出结果:
| LOTID | SOMETEXT | COL | VALUE |
--------------------------------------------
| 1 | Hello | attributeid_1 | 1 |
| 1 | Hello | LotId_1 | 1 |
| 1 | Hello | Value_1 | Foo1 |
| 1 | Hello | Kind_1 | Kind1 |
| 1 | Hello | attributeid_2 | 2 |
我向内部子查询添加了一个 row_number()
以用于创建新的列名称以进行透视。创建名称后,可以将数据透视表应用于新列以给出最终结果
这也可以使用动态 SQL 来完成:
DECLARE @cols AS NVARCHAR(MAX),
@query AS NVARCHAR(MAX)
select @cols = STUFF((SELECT ',' + QUOTENAME(col+'_'+rn)
from
(
select
cast(ROW_NUMBER() over(partition by l.lotid order by a.attributeid) as varchar(10)) rn
from Lot l
left join Attribute a
on l.LotId = a.LotId
) t
cross apply (values ('attributeid', 1),
('LotId', 2),
('Value', 3),
('Kind', 4)) c (col, so)
group by col, rn, so
order by rn, so
FOR XML PATH(''), TYPE
).value('.', 'NVARCHAR(MAX)')
,1,1,'')
set @query = 'SELECT LotId,
SomeText,' + @cols + '
from
(
select LotId,
SomeText,
col+''_''+CAST(rn as varchar(10)) col,
value
from
(
select l.LotId,
l.SomeText,
cast(a.AttributeId as varchar(8)) attributeid,
cast(a.LotId as varchar(8)) a_LotId,
a.Val,
a.Kind,
ROW_NUMBER() over(partition by l.lotid order by a.attributeid) rn
from Lot l
left join Attribute a
on l.LotId = a.LotId
) src
cross apply
(
values (''attributeid'', attributeid),(''LotId'', a_LotId), (''Value'', Val), (''Kind'', Kind)
) c (col, value)
) x
pivot
(
max(value)
for col in (' + @cols + ')
) p '
execute(@query)
所有三个版本都会给出相同的结果:
| LOTID | SOMETEXT | ATTRIBUTEID_1 | LOTID_1 | VALUE_1 | KIND_1 | ATTRIBUTEID_2 | LOTID_2 | VALUE_2 | KIND_2 | ATTRIBUTEID_3 | LOTID_3 | VALUE_3 | KIND_3 |
-----------------------------------------------------------------------------------------------------------------------------------------------------------
| 1 | Hello | 1 | 1 | Foo1 | Kind1 | 2 | 1 | Foo2 | Kind2 | (null) | (null) | (null) | (null) |
| 2 | World | 3 | 2 | Bar1 | Kind1 | 4 | 2 | Bar2 | Kind2 | 5 | 2 | Bar3 | Kind3 |
关于sql-server - 如何替换一个功能性的(很多)OUTER APPLY (SELECT * FROM),我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/15365367/