SQL

Moving Average in SQL (and beyond)

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A very common analytics technique for financial and other data is to calculate the moving average. This can allow you to see a different type of pattern in your data that may not is evident from examining the original data.

But how can we calculate the moving average in SQL?

Well, there isn’t a function to do it, but we can use the windowing feature of analytical SQL to do so. The following example was created in an Oracle Database but the same SQL (more or less) will work with most other SQL databases.

SELECT month, 
       SUM(amount) AS month_amount,
       AVG(SUM(amount)) OVER
          (ORDER BY month ROWS BETWEEN 3 PRECEDING AND CURRENT ROW) AS moving_average
FROM  sales
GROUP BY month
ORDER BY month;

This gives us the following with the moving average calculated based on the current value and the three preceding values, if they exist.

    MONTH MONTH_AMOUNT MOVING_AVERAGE
---------- ------------ --------------
         1     58704.52       58704.52
         2      28289.3       43496.91
         3     20167.83       35720.55
         4      50082.9     39311.1375
         5     17212.66     28938.1725
         6     31128.92     29648.0775
         7     78299.47     44180.9875
         8     42869.64     42377.6725
         9     35299.22     46899.3125
        10     43028.38     49874.1775
        11     26053.46      36812.675
        12     20067.28      31112.085

In some analytic languages and databases, they have included a moving average function. For example using HiveMall on Hive we have.

SELECT moving_avg(x, 3) FROM (SELECT explode(array(1.0,2.0,3.0,4.0,5.0,6.0,7.0)) as x) series;

If you are using Python, there is an inbuilt function in Pandas.

rolmean4 = timeseries.rolling(window = 4).mean()
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How long does it take to build a Machine Learning model using Oracle Cloud

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Everyday someone talks about the the processing power needed for Machine Learning, and the vast computing needed for these tasks. It has become evident that most of these people have never created a machine learning model. Never. But like to make up stuff and try to make themselves look like an expert, or as I and others like to call them a “fake expert”.

When you question these “fake experts” about this topic, they huff and puff about lots of things and never answer the question or try to claim it is so difficult, you simply don’t understand.

Having worked in the area of machine learning for a very very long time, I’ve never really had performance issues with creating models. Yes most of the time I’ve been able to use my laptop. Yes my laptop to build models large models. In a couple of these my laptop couldn’t cope and I moved onto a server.

But over the past few years we keep hearing about using cloud services for machine learning. If you are doing machine learning you need to computing capabilities that are available with cloud services.

So, the results below show the results of building machine learning models, using different algorithms, with different sizes of data sets.

For this test, I used a basic cloud service. Well maybe it isn’t basic, but for others they will consider it very basic with very little compute involved.

I used an Oracle Cloud DBaaS for this experiment. I selected an Oracle 18c Extreme edition cloud service. This comes with the in-database machine learning option. This comes with 1 OCPUs, 7.5G Memory and 170GB storage. This is the basic configuration.

Next I created data sets with different sizes. These were based on one particular data set, as this ensures that as the data set size increases, the same kind of data and processing required remained consistent, instead of using completely different data sets.

The data set consisted of the following number of records, 72K, 660K, 210K, 2M, 10M and 50M.

I then created machine learning models using Decisions Tree, Naive Bayes, Support Vector Machine, Generaliszd Linear Models (GLM) and Neural Networks. Yes it was a typical classification problem.

The following table below shows the length of time in seconds to build the models. All data preparations etc was done prior to this.

Note: It should be noted that Automatic Data Preparation was turned on for these algorithms. This performed additional algorithm specific data preparation for each model. That means the times given in the following tables is for some data preparation time and for building the models.

ml_on_dbaas_1

Converting the above table into minutes.

ml_on_dbaas_2

It is clear that the Neural Network model takes a lot longer to build than all the other algorithms. In this test the Neural Network model had only one hidden layer.
When we chart the build timings, leaving out Neural Networks, we get.
ml_on_dbaas_3 
We can see Naive Bayes, Decision Tree, GLM and SVM algorithms have very similar model build timings, but as the data volumes increase the Decision Tree algorithm become less efficient.
Overall it doesn’t take a long time to build models. In a way it is a very trivial task!
I mentioned at the start of this post I had created a data set of 50M records. Unfortunately I wasn’t able to get models build for this data set using this cloud instance. It used used so much TEMP tablespace that the file volumes on my cloud instance ran out of space!
I suppose if I wanted to go bigger with my data, I needed a bigger boat!
I haven’t included any timings for model scoring using these models. Why? the scored data is immediately returned event for large the largest data sets.

 

RandomForests in R, Python and SQL

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I recently wrote a two part article explaining how Random Forests work and how to use them in R, Python and SQL.

These were posted on ToadWorld webpages. Check them out.

Part 1 of article

https://blog.toadworld.com/2018/08/31/random-forest-machine-learning-in-r-python-and-sql-part-1

 

Part 2 of article

https://blog.toadworld.com/2018/09/01/random-forest-machine-learning-in-r-python-and-sql-part-2

R vs Python vs SQL for Machine Learning (Infographic)

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Next week I’ll be giving several presentation on machine learning at Oracle Open World and Oracle Code One. In one of these presentation an evaluation of using R vs Python vs SQL will be given and discussed.

Check out the infographic containing the comparisons.

Info Graphic

 

OUG Ireland 2017 Presentation

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Here are the slides from my presentation at OUG Ireland 2017. All about running R using SQL.

Presentations from OUGN17

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Here are the presentations I gave at OUG Norway last week. These are also available on SlideShare

Formatting results from ORE script in a SELECT statement

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This blog post looks at how to format the output or the returned returns from an Oracle R Enterprise (ORE), user defined R function, that is run using a SELECT statement in SQL.

Sometimes this can be a bit of a challenge to work out, but it can be relatively easy once you have figured out how to do it. The following examples works through some scenarios of different results sets from a user defined R function that is stored in the Oracle Database.

To run that user defined R function using a SELECT statement I can use one of the following ORE SQL functions.

  • rqEval
  • rqTableEval
  • rqGroupEval
  • rqRowEval

For simplicity we will just use the first of these ORE SQL functions to illustrate the problem and how to go about solving it. The rqEval ORE SQL function is a generate purpose function to call a user defined R script stored in the database. The function does not require any input data set and but it will return some data. You could use this to generate some dummy/test data or to find some information in the database. Here is noddy example that returns my name.

BEGIN
   --sys.rqScriptDrop('GET_NAME');
   sys.rqScriptCreate('GET_NAME',
      'function() {
         res<-data.frame("Brendan")
         res
         } ');
END;

To call this user defined R function I can use the following SQL.

select *
from table(rqEval(null,
                  'select cast(''a'' as varchar2(50))  from dual',
                  'GET_NAME') );  

For text strings returned you need to cast the returned value giving a size.

If we have a numeric value being returned we can don’t have to use the cast and instead use ‘1’ as shown in the following example. This second example extends our user defined R function to return my name and a number.

BEGIN
   sys.rqScriptDrop('GET_NAME');
   sys.rqScriptCreate('GET_NAME',
      'function() {
         res<-data.frame(NAME="Brendan", YEAR=2017)
         res
         } ');
END;

To call the updated GET_NAME function we now have to process two returned columns. The first is the character string and the second is a numeric.

select *
from table(rqEval(null,
                  'select cast(''a'' as varchar2(50)) as "NAME", 1 AS YEAR  from dual',
                  'GET_NAME') );                  

These example illustrate how you can process character strings and numerics being returned by the user defined R script.

The key to setting up the format of the returned values is knowing the structure of the data frame being returned by the user defined R script. Once you know that the rest is (in theory) easy.