Sql Server 2005上的查詢優化

Question

我們在Sql Server 2005上有兩個相關的表（inventory和inventoryLocalization）。第一個表的腳本。

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]

我們有一個查詢取決於這兩個，如下：

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';

如你所知，我們用[language] ='en'選擇所有記錄但如果沒有'en'記錄，則查詢采用'de'（默認）。 但該查詢需要更長的時間（大約13秒）。

你認為任何其他優雅的方法可以減少相同的結果嗎？

提前感謝您提供的任何幫助。

Answer 1

可能很慢，因為當case語句評估null並運行子查詢時，它必須按需執行查詢。

也許這會更快，總是連接到'de'而不是每次找到null時都進行查詢。

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'

Answer 2

select i.code
      ,coalesce(en.language, de.language) as language
      ,coalesce(en.name, de.name) as name
  from inventory i
  left join inventoryLocalization en on(i.code = en.code and en.language = 'en')
  left join inventoryLocalization de on(i.code = de.code and de.language = 'de');

Answer 3

試試這個：

select  i.[code],
        iL.[language], 
        coalesce(il.[name],il2.[name],'Unknown') 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'