优化左加入大量数据的选择查询的SQL

Question

我想知道是否有处理下列情况更快，更好的方式：

我现在发现自己努力优化一个漫长的选择的执行时间查询，我需要为每个记录的每个唯一字段进行左连接（基本上旋转表）。是否有一种方法可以通过单个连接/数据透视将其最小化，以减少检索数据所需的时间？

我需要作出规定，50个自定义字段，超时的30000多条记录（这是与相关列索引）

我希望得到任何帮助（包括修正标题为我不知道如何说明，否则）预先感谢。

下面是代码设置一个小例子：

Create Table CustomField (
ID int identity (1,1) Not Null, 
FieldName varchar(50) Not null, 
FieldOrderNumber int Not Null); 

ALTER TABLE [dbo].[CustomField] ADD CONSTRAINT [PK_CustomField] PRIMARY KEY CLUSTERED 
(
[ID] ASC 
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, IGNORE_DUP_KEY = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON, FILLFACTOR = 90) ON [PRIMARY] 

GO

Create Table FieldValue (
ID int identity (1,1) Not Null, 
CustomFieldID int Not Null, 
PersonID int Not Null, 
FieldValue varchar(50)); 

ALTER TABLE [dbo].[FieldValue ] ADD CONSTRAINT [PK_FieldValue] PRIMARY KEY CLUSTERED 
(
[ID] ASC 
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, IGNORE_DUP_KEY = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON, FILLFACTOR = 90) ON [PRIMARY] 

GO

Create Table Person (
ID int identity (1,1) Not Null, 
PersonName varchar (50) Not Null); 

ALTER TABLE [dbo].[Person] ADD CONSTRAINT [PK_Person] PRIMARY KEY CLUSTERED 
(
[ID] ASC 
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, IGNORE_DUP_KEY = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON, FILLFACTOR = 90) ON [PRIMARY] 

GO

Insert into Person (PersonName) 
Values ('Marc'); 

Insert into Person (PersonName) 
Values ('John'); 

Insert into CustomField (FieldName, FieldOrderNumber) 
Values ('BloodType',1); 

Insert into CustomField (FieldName, FieldOrderNumber) 
Values ('EyeColour',2); 

Insert into FieldValue (CustomFieldID , PersonID, FieldValue) 
Values (1,1, 'A+'); 

Insert into FieldValue (CustomFieldID , PersonID, FieldValue) 
Values (1,2, 'O-'); 

Insert into FieldValue (CustomFieldID , PersonID, FieldValue) 
Values (2,1, 'Blue'); 

Insert into FieldValue (CustomFieldID , PersonID, FieldValue) 
Values (2,2, 'Hazel'); 



WITH ListFieldValues (FieldOrderNumber, FieldName, PersonID, FieldValue) 
AS 
(
SELECT cf.FieldOrderNumber, cf.FieldName, fv.PersonID, fv.FieldValue 
FROM CustomField cf LEFT JOIN FieldValue fv ON cf.ID = fv.CustomFieldID 
) 


SELECT p.ID, 
    p.PersonName, 
    lvf.FieldValue AS Column1, --Bloodtype 
    lvf2.FieldValue as Column2 --EyeColour  
FROM Person p 
LEFT JOIN ListFieldValues lvf ON p.ID = lvf.PersonID and lvf.FieldOrderNumber =1 
LEFT JOIN ListFieldValues lvf2 on p.ID = lvf2.PersonID and lvf2.FieldOrderNumber = 2 

Answer 1

首先，您需要在标识列上创建索引。然后在您要加入的列上创建索引。这些提示将改善您的执行时间。