A Beginner’s Guide to DDL and DML in SQL

Ngetich — Sun, 12 Apr 2026 17:08:24 +0000

Introduction

Structured Query Language or SQL as is commonly referred to is the language used in interacting with relational databases. It allows users to create databases, store data, retrieve data, and modify existing records in a database. SQL commands can be put into categories based on their functionality or how they affect the database. These categories are:

DDL - Data Definition Language
DML - Data Manipulation Language
DQL - Data Query Language
TCL - Transaction Control Language
DCL - Data Control Language

In this article, we look at DDL and DML

DDL, DML and their differences

Data Definition Language (DDL) consists of SQL commands used to define and manage the structure of a database. These commands are responsible for creating, modifying, and deleting database tables and schemas. Common DDL commands include:

CREATE
ALTER
DROP
TRUNCATE

On the other hand, Data Manipulation Language (DML) is used to manage and manipulate the data stored within the database tables. Common DML commands include:

INSERT
UPDATE
DELETE

The main difference between DDL and DML is that DDL deals with the structure of the database, while DML deals with the data inside the database.

DDL and DML commands use cases in SQL

How to Use CREATE

The CREATE TABLE statement is used to create a new table in a database. The syntax of the command is

create table table_name( column1 datatype constraint, columnN datatype constraint );

create table if not exists students( student_id int primary key, first_name varchar(50) not null, last_name varchar(50) not null, gender char(1), date_of_birth date, class varchar(10), city varchar(50) );

This command creates a table named Students with 7 columns - student_id, first_name, last_name, gender, date_of_birth, class and city. Student_id is marked as the primary key, meaning each student must have a unique ID.

How to Use ALTER

The ALTER TABLE statement is used to add, delete, or modify columns in an existing table. It is also used to add or drop various constraints on an existing table.
Common ALTER TABLE operations are:

Add column - Adds a new column to a table
Drop column - Deletes a column in a table
Rename column - Renames a column
Modify column - Changes the data type, size, or constraints of a column
Add constraint - Adds a new constraint
Rename table - Renames a table

For instance, the syntax for adding a column is

alter table students add phone_number varchar(20);

or renaming a column

alter table subjects rename column credits to credit_hours;

or deleting a column

alter table students drop column phone_number;

How to Use INSERT

To add data into the table, the INSERT command is used.

insert into students(student_id,first_name,last_name,gender,date_of_birth,class,city) values (1,'Amina','Wanjiku','F','2008-03-12','Form 3','Nairobi'), (2,'Brian','Ochieng','M','2007-07-25','Form 4','Mombasa'), (3,'Cynthia','Mutua','F','2008-11-05','Form 3','Kisumu'), (4,'David','Kamau','M','2007-02-18','Form 4','Nairobi'), (5,'Esther','Akinyi','F','2009-06-30','Form 2','Nakuru'), (6,'Felix','Otieno','M','2009-09-14','Form 2','Eldoret'), (7,'Grace','Mwangi','F','2008-01-22','Form 3','Nairobi'), (8,'Hassan','Abdi','M','2007-04-09','Form 4','Mombasa'), (9,'Ivy','Chebet','F','2009-12-01','Form 2','Nakuru'), (10,'James','Kariuki','M','2008-08-17','Form 3','Nairobi');

How to Use UPDATE

The UPDATE command is used when you want to modify existing data in a table.

update students set city = 'Nairobi' where student_id = 5;
This changes city of student ID 5 to Nairobi

How to Use DELETE

If a record is no longer needed, the DELETE command can be used to remove it from the table.

delete from exam_results where result_id = 9;
This removes/deletes results id 9 from exam_results table

Filtering with WHERE

When working with databases, it is usually necessary to retrieve or modify only specific records. The WHERE clause allows users to filter data based on specified conditions.
For example, to find all subjects in the Sciences department

select * from subjects where department = 'Sciences';

Several operators can be used with the WHERE clause. Some of these operators include:

= Checks if values are equal

select * from students where gender = 'F';

select * from exam_results where marks = 70;

< or > Compares numerical values (less than/greater than)

select * from exam_results where marks > 70;

BETWEEN Filters values within a range inclusive of the range values

select * from exam_results where marks between 50 and 80;

IN Checks if a value matches any value in the specified column

select * from students where city in ('Nairobi','Mombasa','Kisumu');

LIKE Searches for patterns in text

select * from subjects where subject_name like '%studies%';

The % symbol is a wildcard that can represent any number of characters,i.e,

'A%' means starts with A
'%n' means ends with n
'%ar%' means contains “ar”

How to Use CASE WHEN

The CASE expression is used to define different results based on specified conditions in an SQL statement. It allows users to create conditional logic within queries.

select *, case when marks >= 80 then 'Distinction' when marks >= 60 then 'Merit' when marks >= 40 then 'Pass' else 'Fail' end as performance from exam_results;
This returns the exam_results table with a performance column categorized based on marks

Conclusion

One interesting thing about SQL is that a few simple commands can completely control a database. It is critical to never forget the WHERE clause when using UPDATE or DELETE as this can change or remove every record in a table. Overall, learning DDL and DML provides a strong foundation for working with databases and helps in managing both the structure and the data effectively

How to Publish a Power BI Report and Embed it in a Website

Ngetich — Sun, 05 Apr 2026 12:56:18 +0000

Introduction

Power BI is a powerful tool introduced by Microsoft and widely used for its advanced data analysis capability. It allows users to transform raw data into interactive dashboards and reports that can then be used to derive insights and even aid in decision making.
Among its many functionalities, one could say one of the most important functionality is the ability to publish such reports and dashboards and even embed them to websites for easy sharing and collaboration.
In this article we look at the full process of publishing a power BI report from creating workspaces through to embedding the report in a website.

Step 1: Creating a workspace

Go to Power BI Service (https://app.powerbi.com/)
Follow the sign in steps and use your credentials to sign in to your account
This takes you to the Power Bi Service Home Page.
On the left panel click Workspaces

Click +New Workspace

In the pop up that appears enter:
- Name (Workspace name)
- Description (Workspace description - optional)

Click apply

Your workspace is now created and ready to be used

Step 2: Uploading and Publishing Your Report

Your report can be published from Power BI Desktop or you can upload it directly

Option 1:Publish from Power BI Desktop

Open your report in Power BI Desktop
If you are not already signed in, sign in by clicking on sign in in the top right corner and complete the sign in steps

In the top right of the ribbon, click on Publish

On the pop up, search your workspace name using the search bar

Click Select

Option 2: Direct upload on Power BI Service

On Power BI Service Home page, click on Workspaces on the left panel

Select your workspace or search for it in the search bar

Click on Import - Report, Paginated report or Workbook - from this computer

Browse and Select your file

Your report will now appear in the workspace.

Step 3: Generating the Embed Code

Navigate to your workspace page in Power BI Service and open your Power BI Report by clicking on the name
Click on File - Embed report - Publish to web(public)

Click Create embed code
Copy the generated HTML iframe code

Step 4: Embedding the report on a website

Open your website's HTML file
Paste the copied iframe in the section where you want your report displayed

Save your file and refresh your webpage

Your report is now accessible on your website!

Key Insights

Power BI enables easy sharing of insights on the web through embedding
Workspaces allow users to manage reports in power BI cloud
Embedding uses simple HTML iframes making integration easy

Embedding allows you to turn your reports and dashboards into interactive web experiences. This capability makes your insights more accessible

Forem: Ngetich

A Beginner’s Guide to DDL and DML in SQL

Introduction

DDL, DML and their differences

DDL and DML commands use cases in SQL

How to Use CREATE

How to Use ALTER

How to Use INSERT

How to Use UPDATE

How to Use DELETE

Filtering with WHERE

How to Use CASE WHEN

Conclusion

How to Publish a Power BI Report and Embed it in a Website

Introduction

Step 1: Creating a workspace

Step 2: Uploading and Publishing Your Report

Option 1:Publish from Power BI Desktop

Option 2: Direct upload on Power BI Service

Step 3: Generating the Embed Code

Step 4: Embedding the report on a website

Key Insights