SQL 性能调优

Posted 2020-10-11 pealy

1. Select(1) 优于 Select(*) 

2.In and Exist

in是给外表和内表做hash链接,而Exist是对外表做Loop循环,每次loop循环再做内表查询,如果两个表大小相似,in和Exists差别不大.

如果两个表中一个表大一个表小,子查询大的用Exist,子查询小的用in.

3.计算表中指定时间段的行数,通过先挑出这段时间的最大最小值 然后count(id),如下:DataPointPerSensor.sql (33 minutes) DPNumberPerSensor.sql(16 minutes)

DataPointPerSensor.sql

--this script used to calculate different sensor type of datapoint
select
count(Mll.ID) as [Loc]
from [Tracks].[dbo].[MonitorLocationLog] MLL
where MLL.RowCreatedOn >= ‘2016-01-01‘ 
and MLL.RowCreatedOn <= ‘2017-01-01‘ 

select 
count(1) as [Latitude]
from [Tracks].[dbo].[MonitorSensorLog] MSL
where msl.SensorType=‘Latitude‘ and 
MSL.RowCreatedOn >= ‘2016-01-01‘ 
and MSL.RowCreatedOn <= ‘2017-01-01‘

select 
count(1) as [TemperatureExternal]
from [Tracks].[dbo].[MonitorSensorLog] MSL
where msl.SensorType=‘TemperatureExternal‘ and 
MSL.RowCreatedOn >= ‘2016-01-01‘ 
and MSL.RowCreatedOn <= ‘2017-01-01‘

select 
count(1) as [TemperatureInternal]
from [Tracks].[dbo].[MonitorSensorLog] MSL
where msl.SensorType=‘TemperatureInternal‘ and 
MSL.RowCreatedOn >= ‘2016-01-01‘ 
and MSL.RowCreatedOn <= ‘2017-01-01‘


select 
count(1) as [BatteryExternal]
from [Tracks].[dbo].[MonitorSensorLog] MSL
where msl.SensorType=‘BatteryExternal‘ and 
MSL.RowCreatedOn >= ‘2016-01-01‘ 
and MSL.RowCreatedOn <= ‘2017-01-01‘



select 
count(1) as [BatteryInternal]
from [Tracks].[dbo].[MonitorSensorLog] MSL
where msl.SensorType=‘BatteryInternal‘ and 
MSL.RowCreatedOn >= ‘2016-01-01‘ 
and MSL.RowCreatedOn <= ‘2017-01-01‘

select 
count(1) as [Rssi]
from [Tracks].[dbo].[MonitorSensorLog] MSL
where msl.SensorType=‘Rssi‘ and 
MSL.RowCreatedOn >= ‘2016-01-01‘ 
and MSL.RowCreatedOn <= ‘2017-01-01‘


select 
count(1) as [Motion]
from [Tracks].[dbo].[MonitorSensorLog] MSL
where msl.SensorType=‘Motion‘ and 
MSL.RowCreatedOn >= ‘2016-01-01‘ 
and MSL.RowCreatedOn <= ‘2017-01-01‘


select 
count(1) as [MotionInferred]
from [Tracks].[dbo].[MonitorSensorLog] MSL
where msl.SensorType=‘MotionInferred‘ and 
MSL.RowCreatedOn >= ‘2016-01-01‘ 
and MSL.RowCreatedOn <= ‘2017-01-01‘

View Code

DPNumberPerSensor.sql

--this script used to calculate different sensor type of datapoint
declare @firstLocID nvarchar(100)
declare @lastLocID nvarchar(100)
declare @firstSensorID nvarchar(100)
declare @lastSensorID nvarchar(100)


set @firstLocID=(select top 1 (ID) from [Tracks].[dbo].[MonitorLocationLog] MLL
where mll.RowCreatedOn>=‘2016-01-01‘
order by id)

set @lastLocID=(select top 1(ID) as lastID from [Tracks].[dbo].[MonitorLocationLog] MLL
where mll.RowCreatedOn<=‘2017-01-01‘
order by id desc)


set @firstSensorID=(select top 1 (ID) from [Tracks].[dbo].[MonitorSensorLog] MSL
where MSL.RowCreatedOn>=‘2016-01-01‘
order by id)

set @lastSensorID=(select top 1(ID) as lastID from [Tracks].[dbo].[MonitorSensorLog] MSL
where MSL.RowCreatedOn<=‘2017-01-01‘
order by id desc)

begin

select
count(Mll.ID) as [Loc]
from [Tracks].[dbo].[MonitorLocationLog] MLL
where MLL.ID >= @firstLocID
and MLL.ID <= @lastLocID 


select 
count(1) as [TemperatureExternal]
from [Tracks].[dbo].[MonitorSensorLog] MSL
where msl.SensorType=‘TemperatureExternal‘ and 
MSL.ID >= @firstSensorID
and MSL.ID <= @lastSensorID 

select 
count(1) as [TemperatureInternal]
from [Tracks].[dbo].[MonitorSensorLog] MSL
where msl.SensorType=‘TemperatureInternal‘ and 
MSL.ID >= @firstSensorID
and MSL.ID <= @lastSensorID 


select 
count(1) as [Light]
from [Tracks].[dbo].[MonitorSensorLog] MSL
where msl.SensorType=‘Light‘ and 
MSL.ID >= @firstSensorID
and MSL.ID <= @lastSensorID 

select 
count(1) as [BatteryExternal]
from [Tracks].[dbo].[MonitorSensorLog] MSL
where msl.SensorType=‘BatteryExternal‘ and 
MSL.ID >= @firstSensorID
and MSL.ID <= @lastSensorID 



select 
count(1) as [BatteryInternal]
from [Tracks].[dbo].[MonitorSensorLog] MSL
where msl.SensorType=‘BatteryInternal‘ and 
MSL.ID >= @firstSensorID
and MSL.ID <= @lastSensorID 

select 
count(1) as [Rssi]
from [Tracks].[dbo].[MonitorSensorLog] MSL
where msl.SensorType=‘Rssi‘ and 
MSL.ID >= @firstSensorID
and MSL.ID <= @lastSensorID 


select 
count(1) as [Motion]
from [Tracks].[dbo].[MonitorSensorLog] MSL
where msl.SensorType=‘Motion‘ and 
MSL.ID >= @firstSensorID
and MSL.ID <= @lastSensorID 


select 
count(1) as [MotionInferred]
from [Tracks].[dbo].[MonitorSensorLog] MSL
where msl.SensorType=‘MotionInferred‘ and 
MSL.ID >= @firstSensorID
and MSL.ID <= @lastSensorID

end 

View Code

4.Union VS Union All
Union:对两个结果集进行并集操作,不包括重复行,同时进行默认规则的排序。

Union All:对两个结果集进行并集操作,包含重复行,不进行排序。

INTERSECT:是两个查询结果的交集 对两个结果集进行交集操作，不包括重复行，重复的会被过滤，同时进行默认规则的排序。

Minus:对两个结果集进行差操作，返回的总是左边表中的数据且不包括重复行，重复的会被过滤，同时进行默认规则的排序。

来看下列：表scfrd_type

id         code

1             A

2             B

表scfrd_type1

id         code

2             B

3             C

查询语句select id,code fromscfrd_type  union select id,code from scfrd_type1。结果过滤了重复的行，如下：

id         code

1             A

2             B

3             C

查询语句select id,code fromscfrd_type  union  all select id,code from scfrd_type1。结果没有过滤了重复的行，如下：

id         code

1             A

2             B

2             B

3             C

查询语句select id,code fromscfrd_type  intersect select id,code from scfrd_type1。结果如下：

id         code

2             B

查询语句select id,code fromscfrd_type minus select id,code from scfrd_type1。结果如下：

id         code

1             A