DEV Community: Raymond Anyanzwa

SQL Joins

Raymond Anyanzwa — Sat, 19 Sep 2026 09:47:10 +0000

What is SQL joins

A SQL joins are operations that combine rows from two or more tables based on a related column.

Types of SQL joins

1.Inner join - joins only rows that match in both tables.

2.Left join - All rows from the left matches from the right

3.Right join - All rows from the right matches from the left

4.Self join - A table joined to itself

Conclusion

Joins are one of the most powerful features of SQL in that they allow the data stored in separate tables to be combined into meaningful and useful reports for analysis and decision making.

SQL Fundamentals : DDL AND DDM

Raymond Anyanzwa — Sun, 13 Sep 2026 13:59:23 +0000

What is DDL

DDL stands for Data Definition Language. DDL is a set of SQL commands that are used to define and modify the structure of database objects.
DDL impacts on the creation and maintenance of tables, schemas and indexes.

Key commands in DDL

Create - is used to create new database objects such as tables, views and index.

2.Alter table - Changes the structure of an existing database object by adding, removing or changing columns and constraints.

3.Drop - Deletes a database object permanently

4.Truncate- deletes all rows of data from a table

What is DML

DML Stands for Data Manipulation Language. DML is used to interact with and modify the data stored inside tables.

Key commands of DML

1.Insert - add new records in a database table.

2.Update - updates existing records in a database table.

3.Delete - removes rows in a database table

4.Select - displays one or more tables in a database.

Conclusion

DDL defines the structure of your database while DML manages the data inside that structure.

Why Python Is Used In The Data Field?

Raymond Anyanzwa — Thu, 03 Sep 2026 15:47:14 +0000

Introduction

The first line of code I wrote in python was
print("Hello world")

This would lead me to discovering that python is used to do numerus tasks that aid people in the data field to do the following:

create data pipelines
design machine learning models
create dashboard

Why do people in the data space choose python

Python has simple syntax which reads like plain English.
Python has powerful libraries like pandas, numpy, matplotlib and py torch which helps in data manipulation and machine learning.
Python has a massive community that allows meaningful quick answers to be accessed by data workers.

Lets learn python

variables are a labeled box where you store a piece of information

name = "Ray" 
age = 19
city = 'Nairobi'
height = 190.8
is_active = True

Python has 4 types of data types

String name = "Ray" - Ray is the string that is stored in the variable called name.
Integer age = 19 - 19 is the integer that is stored in the variable called age.
Float height = 190.8 - 190.8 is the float that is stored in the variable called height.
Bool is_active = True - True is the boolean state that is stored in the variable called is_active.

Python has 4 operators

Comaprisson operator - compares two values and gives you true or false

age = 19
print(age > 19) ---> False 
print(age == 19) ---> True

Logic operators - includes and, or , not and - true if both conditions are true or - true if one condition is true not - turns true to false

if, elif, else

Nested if

Conclusion

If you are new to data, Python is the best place to begin because python takes a short time to code and also informs and where there is a mistake.

RELATIONSHIP SCHEMA AND JOINS

Raymond Anyanzwa — Sun, 28 Jun 2026 18:06:06 +0000

Power BI is built in relationships. A well designed relationship schema enables accurate calculations and efficient analysis.

What is a relationship schema A relationship schema describes how tables in your model are connected. With these relationships Power BI can combine data from multiple tables. Tables are related using columns.

Types of relationship schema

One to one one record correspondence between the first and the second table.
One to many One record in the first table can link to multiple records in the second table.
Many to many
Records in one table are related to multiple records in another table.
JOINS
Joins are used to combine data from two tables before its loaded in the model.

Types of joins
1.Inner join- Returns matching rows from both tables
2.Full join/full outer join- all rows from both tables matched or unmatched.
3.Left join/Left outer join- all rows from the left table match with the right table.
4.Right join/ right outer join- all rows from the right table match with the left table.
5.Left anti join-All rows from the left table with no match to the right table.
6.Right anti join- All rows from the right table with no match to the right table.

How Excel is Used in Real-World Data Analysis

Raymond Anyanzwa — Fri, 05 Jun 2026 21:18:23 +0000

I started studying about excel when when i was in high school. Ever since i liked working on excel Excel is a spreadsheet that allows you to analyze, collect, visualize and calculate data.It is mostly used for both professional and personal data management.
Excel consists of elements:
1.Rows -are labelled in numbers(1,2,3)
2.Columns -are labelled in Alphabets (A,B,C)
3.Name box- its show the name of the selected cell(B1)
4.Worksheet tabs -this are found at the bottom(Sheet 1)
5.Cell- is the rectangle formed where a column and a row meet(B1)
6.Data tools-These are tools that are used to manipulate data(sorting, filtering)
7.Functions and formulas- Functions are used to calculate automatically(sum(),Avg() while formulas are instructions given given to perform a piece of data(+,-,*,/)

Excel is used in real world data by analysis by:
1.Data cleaning
Data cleaning helps by splitting combined text, removing duplicates, formatting(find and replace) and ensuring numbers, dates, currency are well formatted.

2.Organizing data
Many companies,schools and hospitals structure its tables using columns(Name,Region,Age,Gender)

3.Business decision
Many business make decisions by planning promotions based on the sale trend and focus on products that makes the most revenue.

Formula makes it easy when calculating values of the cell.In formula you have to start with an (=) or it will not work.Examples of formulas
1.Sum()- we use it to calculate the total values =sum(B2:B14)
2.Avg()-we use it to find the average =Avg(B2:B14)
3.Datedif()- we can use it to find the difference in months ,days and years.Datedif in years =Datedif(C2:C14,"y"),in months =Datedif(C2:C14,"m") and in days =Datedif(C2:c14,"d").

In conclusion excel has helped in me in organizing data, cleaning data, data visualization,how to use new formulas that i didn't study in high school like "datedif","sumif" and "avgif" and the using of tools. Excel has showed how it is meaningful in business.