By: Dallas Snider | Updated: 2015-02-11 | Comments | Related: > TSQL
Problem
In SQL Server data mining, we sometimes need to perform techniques such as decimal scaling normalization on numeric data type columns to prevent one column from skewing or dominating the models produced by the machine learning algorithms.
Solution
In this tip, we will demonstrate how to use T-SQL to perform a decimal-scaling normalization in SQL Server. To perform the decimal scaling, we must first calculate the next largest integer from the base-10 log of the maximum value in the column. Then we divide the original column value by 10 raised to this calculated value to get our normalized value. We will use T-SQL's MAX() function to find the maximum value in the column, the LOG10() function to get the power of 10 to which the column value is raised, the CEILING() function to give us the next largest integer, and the POWER() function to calculate the divisor.
We will create a table that contains two data columns, AttributeX and AttributeY, and perform the decimal scaling normalization on each of these columns.
IF EXISTS (SELECT name FROM sys.tables WHERE name = N'tblExample') DROP TABLE dbo.tblExample go create table dbo.tblExample ( pKey integer identity(1,1) PRIMARY KEY, AttributeX decimal(10,3), AttributeY decimal(10,3) )
Next, we will populate this table with 17 rows of data. AttributeY will be 100 times the value of AttributeX.
insert into dbo.tblExample values (2, 200) insert into dbo.tblExample values (30, 3000) insert into dbo.tblExample values (270, 27000) insert into dbo.tblExample values (300, 30000) insert into dbo.tblExample values (310, 31000) insert into dbo.tblExample values (320, 32000) insert into dbo.tblExample values (330, 33000) insert into dbo.tblExample values (360, 36000) insert into dbo.tblExample values (410, 41000) insert into dbo.tblExample values (440, 44000) insert into dbo.tblExample values (460, 46000) insert into dbo.tblExample values (470, 47000) insert into dbo.tblExample values (510, 51000) insert into dbo.tblExample values (560, 56000) insert into dbo.tblExample values (570, 57000) insert into dbo.tblExample values (6300, 630000) insert into dbo.tblExample values (8100, 810000)
After inserting the rows, we will select the next largest integer of the base-10 logarithm of the maximum value of each column.
select ceiling(log10(max(AttributeX))) as nextLargestPowerOf10ForX from dbo.tblExample select ceiling(log10(max(AttributeY))) as nextLargestPowerOf10ForY from dbo.tblExample
We can see the results from the above queries in the image below.
Now we will use the T-SQL code below to perform the decimal-scaling normalizations on AttributeX and AttributeY.
--Declare the variables declare @nextLargestPowerOf10ForX as integer declare @nextLargestPowerOf10ForY as integer --Set the variables set @nextLargestPowerOf10ForX=(select ceiling(log10(max(AttributeX))) from dbo.tblExample) set @nextLargestPowerOf10ForY=(select ceiling(log10(max(AttributeY))) from dbo.tblExample) --Perform the normalization select AttributeX, -- the original Attribute X value (AttributeX/POWER(10, @nextLargestPowerOf10ForX)) as NormalizedX, AttributeY, -- the original Attribute X value (AttributeY/Power(10, @nextLargestPowerOf10ForY)) as NormalizedY from dbo.tblExample
The results from the previous query are shown below. Notice how the normalized values for AttributeX and AttributeY are equal on each row, while the original values differ. Also notice how this process will produce normalized values from zero to one inclusive.
Next Steps
Normalized values can be inserted into a table and then read into data mining algorithms. You can read more about SQL Server data mining in the following tips from MSSQLTips.com.
- SQL Server Min Max Column Normalization for Data Mining
- SQL Server 2012 Analysis Services Association Rules Data Mining Example
- Explaining the Calculations of Probability and Importance for Complex Association Rules in SQL Server 2012 Analysis Services
- Classic Machine Learning Example In SQL Server Analysis Services
- Microsoft Naïve Bayes Data Mining Model in SQL Server Analysis Services
- Data Mining Clustering Example in SQL Server Analysis Services SSAS
- SQL Server Analysis Services Glossary
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This author pledges the content of this article is based on professional experience and not AI generated.
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Article Last Updated: 2015-02-11