Category: Data Analysis

Google Cloud Platform Fundamentals

Google Cloud is seen as a leader in areas including data analytics, machine learning and open source. And digital transformation through the cloud allowed companies to deliver personalised, high quality experiences.

During this Lockdown time in New Zealand, working from home means taking less time on the traffic and a time to learn more advanced techniques.

So stay positive and stay safe!

Thanks to GCP fundamentals, it is a perfect opportunity for those who wants to learn Google Cloud Platform.

If you are interested in or have any problems with Business Intelligence, feel free to contact me.

Or you can connect with me through my LinkedIn.

What is normalization and what are normalization forms?

Normalization is a technique that decomposes the table to reduce the redundacy of data.

There are 3 normalization forms we need to check and follow to normalize tables.

1st Normalization Form:

  1. Each coloum of the table should have a single value
  2. Each column should belong to a same domain
  3. Two colums should not have a same name
  4. It need not to be a proper order, e.g., we need not to sort the records according to the date of DOB.

2nd Normalization Form:

  1. The table should be satisfy 1st Normalization Form
  2. All the non-key attributes myst be functionally dependently on primary key

3rd Normalization Form:

  1. The table should be satisfy 2nd Normalization Form
  2. There is no transitive dependency for non-prime attributes

The transitive functional dependency is as follows:

A is functional dependent on B and B is functional dependent on C. So, C is transitive dependent on A through B.

If you are interested in or have any problems with Business Intelligence, feel free to contact me.

Or you can connect with me through my LinkedIn.

DAX Cheat Sheet

What is DAX?

It is the programming language for Power Pivot, SSAS Tabular and Power BI.

It resembles Excel because it was born in PowerPivot. But it has no concept of <row> and <column> and has different type system.

The most important, it has many new functions.

The most two are measure and calculated column:

Measure is used to calculate aggregates, e.g., Sum, Avg and evaluated in the context of the cell in a report or a DAX query.

Calculated column evaluates each row and is computed at the low level within the table it belongs to.

Some Common Dax Expressions:

LOOKUP:

  1. Return the value in result_columnName for the row that meets all criteria specified by search_columnName and search_value
  2. LOOKUPVALUE(Result Column Name, Search Column Name, Search Column value)

FILTER:

  1. Return a subset of a table or expression
  2. FILTER(<table>,<filter>)

ALL:

  1. Return all the rows in a table, or values in a column, ignoring any filters that may have been applied
  2. ALL(<table> or <column>)

RELATED

  1. Returns a related value from another table
  2. RELATED(<column>)

CALCULATE

  1. Evaluates an expression in a context that is modifies by specific filters
  2. CALCULATE(<expression>,<filter1>,<filter2>)

If you are interested in or have any problems with DAX or Business Intelligence, feel free to contact me.

Or you can connect with me through my LinkedIn.

Agile Scrum Workflow

Scrum is one of the Agile framework:

1 User story and refinement:

Input from executives, team, stakeholders, customers

2 Product Backlog:

Ranked list of what is required: features, stories

3 Sprint Planning Meeting:

Team selects starting at stop as much as it can commit to deliver by end of sprint

4 Sprint Backlog: Task breakout

5 Stand-up meeting: daily discussion between team members

6 Sprint end date and team deliverable do not change

7 Sprint review, finished work and sprint retrospective

If you are interested in or have any problems with Agile or Business Intelligence, feel free to contact me.

Or you can connect with me through my LinkedIn.

How to do web scrapping in Power Query in Power BI?

On web, there are public data sourse which can be imported and transformed to make insight reports or dashboards.

There are two circumstances:

This kind of importing of tables is super easy.

For example, we can try to make an easy one.

Here is the web link: https://en.wikipedia.org/wiki/Demographics_of_China. What we want is to import the tables from a Wikipedia webpage.

The simple steps are as follow:

Open Power BI Desktop–>Click Get Data–>Click Web–> Paste the URL in the dialog and click OK.

So, there is the screenshot:

In Navigatot dialog, we can select the corresponding table that we want to import and transform it.

This kind of importing from web in Power BI is simple. Because Power Query can identify the table in HTML and tables are in the <table>…</table> tags.

However, many tables in HTML are different.

If we meet this kind of circumstance, we will end up seeing the Document entity in the Navigator.

Next blog, we will demonstrate how to extract the relevant elements in HTML with Power Query in Power BI.

The tricky part id how to find the correct path in the HTML source tree, which needs you to have a basic but not prior HTML knowledge.

To motivate you to keep reading, here is the final web scarping screenshot which i made recently:

If you are interested in or have any problems with Power BI or Power Query, feel free to contact me.

Or you can connect with me through my LinkedIn.

Create a SSIS Project in Visual Studio 2015

Installation:

  1. SQL Server Data Tools 2015(install a shell of Visual Studio 2015)
  2. Visual Studio 2015

What is SSIS?

SSIS stands for SQL Server Intergration Services. SSIS is to do the ETL(Extract, Transform and Load) task for data warehouse.

SSIS can also update data warehouse, clean and mine data, create ‘packages’, manipulate data, etc.

To design ETL task in Visual Studio, we use the data flow in Visual Studio.

What is data flow?

A data flow defines a flow of data from a source to a destination.

Before designing the data flow, we can try to drag a data flow and drop it in the control flow.

What is a control flow?

It is a flow we can use to control the flow for different tasks. It provides the logic for when data flow components are run and how they run.

For example:

  1. perform lopping
  2. call stored procedures
  3. move files
  4. manage error handling
  5. check a condition and call different tasks

It defines a workflow of tasks to be executed, often a particular order (assuming your included precedence constraints).

we can rename the data flow task in control flow.

For example, we can drag OLE DB Source, so we can connect to Relational Database.

Then we can follow the Microsoft official toturial to do it step by step.

https://docs.microsoft.com/en-us/sql/integration-services/lesson-1-1-creating-a-new-integration-services-project?view=sql-server-ver15

If you are interested in or have any problems with SSIS, feel free to contact me.

Or you can connect with me through my LinkedIn.

Dimensional Modelling

First of all, a concept of Data Warehouse is supposed to be clear. Data Warehouse is not a copy of source database with a name prefixed with ‘DW’.

DW is we can store data from multiple data sources to be used for historical or analysis report. Some data sources are .csv format, some are google docs, etc. So we need to aggregate them into one data source.

This is called Data Warehouse.

How to design it? The procedure is Dimensional Modelling.

What is the difference between relational and dimensional?

It is same as the difference like normalised VS denormalised.

Normalised:

  1. Minimal data redundancy
  2. Optimised for fast read and fast write
  3. Current data only
  4. Realtime data

Denormalised:

  1. Redundancy data storage for performance
  2. Fast read only
  3. Non-realtime data
  4. Current and historical data

The next part is about fact table and dimension table in dimensional design.

Fact table:

  1. Data that can be measured
  2. Contains surrogate key, linking the associated measures or facts

Dimension table:

  1. Descriptive information

Some types of dimensional models:

  1. Accumalating snapshot table
  2. Aggregate fact
  3. Fact table
  4. Factless Fact table
  5. Snapshot table

If you are interested in or have any problems with Dimensional Modelling, feel free to contact me.

Or you can connect with me through my LinkedIn.

SQL Correlated Subqueries

Recently I often made some mistakes about subqueries, so I wrote this blog about correlated subqueries.

Firstly, here is a SQL practicing website: https://sqlzoo.net.

It is free and easy for SQL beginners to do SQL exercise step by step.

A correlated subquery works like a nested loop: the subquery only has access to rows related to a single record at a time in the outer query.

The technique relies on table aliases to identify two different usages of the same table, which means one usage is in the outer query and another one is in the subquery.

Here is a table called world, which is an example on the sqlzoo website:

namecontinentareapopulationgdp
Afghanistan Asia 652230 25500100 20343000000
Albania Europe 28748 2831741 12960000000
Algeria Africa 2381741 37100000 188681000000
Andorra Europe 468 78115 3712000000
Angola Africa 1246700 20609294 100990000000
… … … … …

Question: Find the largest country (by area) in each continent, show the continent, the name and the area.

SQL answer using subquery: 

SELECT continent, name, area 
FROM world x
WHERE area >= ALL
    (SELECT area FROM world y
     WHERE y.continent=x.continent AND area>0)

One way to interpret the SQL line in the WHERE clause that references the two table is “… where the correlated values are the same”.

In this example, we can tell “select the country details from the world table where the area is larger than or equal to the area of all countries where the continent is the same”.

If you are interested in or have any problems with SQL, feel free to contact me.

Or you can connect with me through my LinkedIn.

An Introduction to Power BI (Power BI 101)

This article we will provide an introduction to Power BI.

It is a Microsoft business analytics service to provide interface to create reports and dashboards with interactive visualisations.

It has an advantage: easy to use (self service BI).

First of all, Power BI official guided learning material.

It’s very structured and good training tutorial.

As I talk in previous blog about this learning platform, it is fun to get points and badge.

What is the workflow of Power BI?

  1. Bring data in using Power BI desktop, manipulate data and build reports.
  2. Publish it to Power BI service.
  3. Share reports and dashboards to others.

Here we go to the first step:

Download the Power BI desktop.

Power BI desktop version provides data warehouse capabilities:

  1. ETL
  2. Calculates column
  3. Measures

After we download it, we can find there are five panels in Power BI interface:

  1. Fields: where the datasets
  2. Data: view and manipulate the data
  3. Reports: place visualizations to build reports
  4. Dashboards: choose the graphs to use
  5. Relationships: view/change relationships in the dataset

Through these panels, we can manipulate data and build reports.

Once the report is completed, we can publish it onto Power BI Service on the cloud.

Reference sources:

https://www.sqlbi.com/ref/power-bi-visuals-reference/

If you are interested in or have any problems with Power BI, feel free to contact me.

Or you can connect with me through my LinkedIn.

The Simplest Way to Understand SCD in Data Warehouse

What is SCD?

SCD stands for Slowly Changing Dimensions.

It is very important in Data Warehouse.

As we know, ETL (Extract, Transform, Load) is between data sources and data warehouse.

When ETL runs, it will pick up all records and update them in the Dimension tables.

Why we need SCD?

Because we have some problems in updating data in Data Warehouse when data in data sources are changing.

In the dimension tables, if we want to keep some old records, how we can do this?

Using SCD.

Types of SCD:

Note：The types of SCD are defined on Column level, not on the table level.

There are two popular types in SCD.

Type 1: Overwrite

An old record is updated by the new record. It means covering the old records.

Type 2: Store history by creating another row

Type 2 is to add new records rather than covering the old records.

As long as we have a type 2 in tables, we must have two extra values: ‘StartDate’ and ‘EndDate’. The ‘EndDate’ is when the changes happen, as the end date of historical data.

We can have a third one, ‘IsCurrent’, to identify or mark the current record.

We don’t need to update the records, and we just need to update ‘StartDate’ and ‘EndDate’.

If you are interested in or have any problems with fact tables and dimension tables, feel free to contact me .