mysql - 优化SQL中大数据的left join select查询

Question

我想知道是否有更快或更好的方法来处理以下情况:

我目前发现自己正在努力优化冗长的选择查询的执行时间，其中我需要为每条记录的每个唯一字段进行左连接(基本上是旋转表)。有没有办法通过单个连接/枢轴来最小化这种情况，以减少检索数据所需的时间？

我需要准备 50 个自定义字段，这会在 30000 条奇数记录上超时(这是在相关列上有索引)

如果有任何帮助(包括更正标题，因为我不确定如何表述)，我将不胜感激。提前致谢。

下面是设置一个小示例的代码:

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]

开始

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]

开始

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]

开始

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。这些技巧将缩短您的执行时间。