DEV Community: Wilfred Odhiambo

Understanding SQL: DDL, DML, Filtering, and CASE WHEN

Wilfred Odhiambo — Wed, 15 Apr 2026 09:16:11 +0000

Background

A few years ago when I was a student at a Kenyan university, I attempted to learn a computer programming language called GW-BASIC. I was thrilled at the beginning due to the logical nature of the language only for things to get ‘tough’ along the way perhaps due to lack of commitment from my side. Fast forward, in year 2026, I have developed an interest to learn a new skill to help me with data analysis and with that, I have the opportunity to study another computer language commonly referred to as SQL.

Introduction

Every time you search for something online, stream a movie, or check your bank balance, there is a database working behind the scenes. In most cases, that database understands one language: SQL. Think of a database as a giant, well organized filing cabinet, and SQL as the set of instructions you use to search through it, add new folders, or remove old ones.

SQL was invented in the 1970s by an IBM scientist and has been refined over the years so that it is used in banks, hospitals, schools, social media platforms, and e-commerce websites.

SQL stands for Structured Query Language. It is a computer language used to store, find, update, and delete information in a database. It is considered a declarative language in that you tell the computer what you want; for example, you say "Give me all sales above KES 10,000" and SQL figures out the rest. This is what has so far made it easy to learn compared to my earlier attempt to learn a computer language.

SQL encompasses data query language (DQL), data definition language (DDL), data control language (DCL), and data manipulation language (DML) covering everything from querying and inserting records to defining schemas and controlling access.

This article together with attached SQL script will demonstrate basic skills to deploy DQL, DDL and DML as a beginner.

What are DDL and DML

SQL commands are broadly grouped into two categories: DDL and DML. While they both operate on a database, they serve very different purposes as summarized below.

In simple terms, DDL shapes the container (the table), while DML manages what goes inside it. You must define the structure first before any data can be stored or retrieved.

CREATE, INSERT, UPDATE & DELETE in Practice

These are four core SQL commands to build and manage a simple database table.

CREATE — Define a new table

The CREATE command establishes the table structure, specifying column names and their data types.

INSERT — Add rows of data

Once the table exists, INSERT populates it with records.

UPDATE — Modify existing records

UPDATE changes values in existing rows. The WHERE clause is essential here — without it, every row would be updated.

DELETE — Remove specific rows

DELETE removes rows that match a condition. Again, WHERE determines which rows are affected.

Filtering with WHERE

The WHERE clause is one of the most powerful tools in SQL. It filters which rows a query acts on; whether you are selecting, updating, or deleting data. Without it, operations apply to every row in the table, often with unintended consequences.

SQL offers a rich set of operators to build flexible filters.

Practical examples illustrating these operators.

The LIKE operator is especially useful for partial text matching. The % symbol acts as a wildcard — 'A%' matches anything starting with "A", while '%son' matches anything ending in "son".

Transforming Data with CASE WHEN

CASE WHEN is SQL's version of an if-else statement.

It lets you create new labels or categories on the fly, directly within a query without changing any data in the table.

See below example used to convert numeric scores into descriptive performance labels.

This is incredibly useful for reporting and dashboards. Rather than storing a "performance" column in the database, you compute it dynamically based on the current scores. It keeps the data clean and the logic flexible.

Reflection

The most interesting part is realizing how much the WHERE clause changes the meaning of a query. The same DELETE or UPDATE statement becomes safe or catastrophic depending on whether you include it. The main challenge is dealing with syntax errors which slows down the learning process. In many occasions, I have had to rely on other AI tools to help me identify mistakes in the scripts which I believe is part of learning process.

How to Publish a Power BI Report and Embed it into a Website.

Wilfred Odhiambo — Sun, 05 Apr 2026 18:24:21 +0000

Background

In my last article titled ‘How Excel is Used in Real-World Data Analysis’ dated 26th March, 2026 and published through my Dev.to account, I had shared the frustrations my workmates and I were going through when end of year 2025 performance appraisal results of all employees in the department plus departmental head’s recommendations for individual employee promotion were rejected by company directors. The performance appraisal results and recommendations were rejected with one comment, “the department has not presented any dashboard to demonstrate individual employee’s productivity, improvements on performance measures and so on to justify promotions or any rewards.’

In the article which is accessible through my blog https://dev.to/mckakankato/excel-3ikf, I attempted to create simple dashboard using excel application which could have been used to monitor one Key Performance Indicator (KPI) on monthly basis, may have been used to measure performance and most importantly, may have been shared with the company directors to provide feedback on how performance was being tracked in the department.

Excel application is an excellent tool and with recent enhancements, it is more than just as a spreadsheet tool since the intelligent data platform capabilities enable automation of analysis, connecting to live external data sources and so on hence transforming how professionals work with data. However, Microsoft introduced another powerful tool called Power BI which has capabilities of handling large datasets with much ease and also publish dashboards online where decision makers can access by just a click of a link. Power BI’s ability to allow real time updates on data and on the dashboard sets it apart from the excel application. Moreover, one can access reports on web, mobile, or embedded in other apps. The mobile app version especially allows access to Power BI reports on the go using an iPhone or Android device hence eliminating the need to carry laptops or tablets to every meeting.

This article will provide a guide on how to publish Power BI dashboard that can be accessed by stakeholders in real time to aid in timely decision making.

Introduction

‘Power BI’ is drawn from two phrases put together that is ‘Power’ and ‘BI’ referring to Business Intelligence.

The developers seem to be communicating that the application draws its power from the tool’s capability to handle large, complex datasets and perform powerful data transformations, modeling, and analysis beyond what traditional spreadsheets could manage. The business intelligence capability refers to the technologies, processes, and strategies used to collect, analyze, and present business data in ways that support better decision making. Business Intelligence typically encompasses dashboards, reports, data visualization, KPIs, and trend analysis. Power BI therefore essentially means a powerful tool for turning raw business data into meaningful insights giving organizations the ability to connect to hundreds of data sources, model and transform data, and visualize it through interactive dashboards and reports.

This tool has been around from the year 2010 when its development commenced. Among the key features announced at the early stages included Power Query for data search and discovery from both internal business sources and external internet data, Power Pivot for data modeling, Power View for visualization, BI sites for cloud based collaboration and report sharing and so on. The recent updates positions Power BI not just as a data visualization tool but as a comprehensive, AI-driven business intelligence platform with hundreds of features spanning data connectivity, semantic modeling, DAX formula authoring, interactive dashboards, real-time reporting among others.

Examples of industries that would benefit most from Power BI include Financial Services & Banking, Healthcare, Retail & E-Commerce, Manufacturing & Supply Chain, Telecommunications, education and Government. Power BI is a natural fit to aid in monitoring financial statements KPIs instantly, undertake complex computations through DAX formular, track patient outcomes, real time inventory tracking, monitor production efficiency, manage Telecom companies’ massive volumes of customer, network, and billing data as well as student performance tracking.

Power Bi Dashboard & Report Publication Process

Once you have cleaned your report through Power Query, modelled the data so as to create relationships, it is time to prepare summarized report with a dashboard which gives decision makers insights. The report & dashboard can be published online to allow users to interact with it on real time basis and from any location. Below steps can guide in publishing Power BI reports.

Open your Power BI Desktop.

Locate the Power BI document in your computer with report the report you intend to publish. Click on Sign in on the far right of the document as shown in the image below. You will need an organization email & password for this.

Proceed and provide the necessary organization email address & password and you should be able to log in.
Through Power BI website, open Power BI Service usually accessible through a link; https://app.powerbi.com/

On the lower left-hand side of the website, locate “Workspaces” or “My workspace”. If the organization has created a workspace for you, it will be accessible in “My work spaces”. Else proceed to create a new one complete with your profile under “workspaces”. An existing workspace will show your profile name as per below.

Import the specific report you intend to publish or add to other past publications.

Once uploaded, click on the file & locate “embed report’ option. This will lead you to ‘website or portal option’.

This will generate two important links to embed the report to website & iframe link to help publish. Copy the two links and paste then separately for use in the next steps.

https://app.powerbi.com/reportEmbed?reportId=eb9d6d81-f7a2-4c54-8ebb-5468e0c1894f&autoAuth=true&ctid=c95984e8-6a70-4512-a440-1c79bca9cc37

Depending on whether you are using “Sublime Text” or VsCode, the second Link “iframe” will be pasted in text editor as per below.

Save the document (Ctr+S) once link is pasted.

Right click on the text editor & open browser as per below.

Another Power BI Service page as per below will open requiring the organizations credentials.

Once credentials are provided, a published report will be accessible as per below.

Conclusion

The reports will be available in real time, from any location and on any device which makes monitoring of performance & decision making based on dashboard insights timely.

How Excel is Used in Real-World Data Analysis

Wilfred Odhiambo — Thu, 26 Mar 2026 15:28:18 +0000

Background

Early January, 2026, we had concluded first stage of employee annual performance appraisal at departmental level. We now awaited feedback from directorate who are in charge of moderation of performance appraisal feedback scores awarded to each employee by the departmental head. The second stage (moderation) considers the overall performance of the organization, the moderation committee ‘opinion’ about the department among other ‘things.’ In late February, 2026, we received a communication rejecting appraisal results of all employees in the department plus departmental head’s recommendations. One comment stood out in the communication; “the department has not presented any dashboard to demonstrate individual employee’s productivity, improvements on performance measures and so on to justify promotions or any rewards’. I then asked myself two questions. If the agreed performance measures are all captured in an online Human Resource Management System application (HRMS) depending on each employee’s Job Description (JD) and the HRMS has computed the employee’ performance scores, which other ‘things’ are being reviewed at moderation stage? Why is the data captured in the application not being used to create dashboards to help answer questions raised at moderation stage? Based on my years of experience, I had always felt that the performance measures as captured in HRMS were general and would not be sufficient to create any dashboards. Using excel application, this article will attempt to create a simple dashboard which could have been used to monitor one Key Performance Indicator (KPI) on monthly basis and may have been used to measure performance. The critical indicator that has direct impact on customer service is Turn Around Time (TAT).

This article is written in fulfilment of an assignment and as such, it is not to be relied on entirely for academic writing.

Introduction

Microsoft Excel (Excel) was introduced in the 1980s and the initial release included features which in today’s standard are considered basic. The features included cell formatting, simple formulas, and charting capabilities. The Excel ease of use and capabilities made it a favourite and popular appli
cation among its users. This background became the foundation for what would become the world’s dorminant spreadsheet application used in almost every industry.

Fast forward, the latest iteration of Excel includes capabilities such as puling live information such as scientific figures, market trends and historical statistics from trusted online sources into a worksheet. It has also introduced a wide range of formulas to help in data manipulations as well as AI-based data cleaning feature to address inconsistent text, number formats, and extra spaces thereby reducing time spent on manual data cleaning. These enhancements position Excel as more than just as a spreadsheet tool since the intelligent data platform capabilities enable automation of analysis, connecting to live external data sources and so on hence transforming how professionals work with data.

Excel Formulas & Features

Excel has well over 500 formulas which are broadly categorized as financial, statistical, logical, text, lookup, engineering, and date/time. Due to ever increasing number of new features being released and added to the software, it has become difficult to keep track of all the updates.

Below monitoring feature was developed using hypothetical statistical data for three months period. A simple ‘nested IF’ formular was used to establish number of credit files reviewed within set TAT and those with delayed TAT. A simple pivot table was extracted from the data to summarized the findings and simple line graph plotted to visualize trend of TAT compliance. Another excel feature; ‘slicer’ was added to make it easier for reviewer to interact with the line graph.

Conclusion

Excel has becoming a tool that can be used to perform more functions and as such, any task which generates, collects or processes data should aim at creating a visual summary inform of a dashboard that communicates or monitors if everything is on track to help achieve a bigger goal.