sql - Sql Server 2005上的查询优化

我们在Sql Server 2005上有两个相关的表(inventory和inventoryLocalization)。
第一个表的脚本。

CREATE TABLE [dbo].[inventory](
    [code] [varchar](35) NOT NULL,
    [salePrice1] [decimal](22, 2) NULL,
 CONSTRAINT [PK_inventory] PRIMARY KEY CLUSTERED
(
    [code] ASC
)WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]
) ON [PRIMARY]

第二个是

CREATE TABLE [dbo].[inventoryLocalization](
    [code] [varchar](35) NOT NULL,
    [language] [varchar](2) NOT NULL,
    [name] [nvarchar](100) NOT NULL,
    [description] [nvarchar](max) NULL,
 CONSTRAINT [PK_inventoryLocalization] PRIMARY KEY CLUSTERED
(
    [code] ASC,
    [language] ASC,
    [name] ASC
)WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]
) ON [PRIMARY]

我们有一个查询依赖于这两个，如下所示:

select  i.[code],
        iL.[language],
        case
        when iL.[name] is null then (select iL2.name  from dbo.inventoryLocalization iL2 where iL2.[language] = 'de' and iL2.code = i.[code])
        else iL.[name]
        end as [name]
from dbo.inventory i
left join dbo.inventoryLocalization iL on i.code = iL.code and iL.[language] =  'en';

如您所料，我们选择[language] ='en'的所有记录，但是如果没有'en'的记录，查询将采用'de'(默认)。
但是该查询需要更长的时间(大约13秒)。

您是否认为任何其他用于达到相同结果的优雅方法都可以减少花费的时间？

在此先感谢您提供的任何帮助。

最佳答案

可能很慢，因为在case语句评估为空并运行子查询时，它必须按需执行查询。

也许这样会更快，请始终执行到“de”的联接，而不是每次发现空值时都执行查询。

select  i.[code],
        iL.[language],
        case
        when iL.[name] is null then iL2.name
        else iL.[name]
        end as [name]
from dbo.inventory i
left join dbo.inventoryLocalization iL on i.code = iL.code and iL.[language] =  'en'
left join dbo.inventoryLocalization iL2 on i.code = iL2.[code] and iL2.[language] = 'de'