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A.Data Exploration & Cleansing.md

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📚 Case Study - Udemy Course: A. Data Exploration and Cleansing

Using Microsoft SQL Server

IMPORT FILE TO SQL

1. Checking duplicates rows by using Group By & Having and delete duplicate rows

SELECT course_title,course_id
FROM udemy_courses
GROUP BY course_title,course_id
HAVING count(course_title)>1 and count(course_id) >1;

Duplicate rows

image

  • Delete duplicate rows
WITH CTE AS
(
SELECT *,ROW_NUMBER() OVER (PARTITION BY course_id,course_title ORDER BY course_id,course_title) AS RN
FROM udemy_courses
)

DELETE FROM CTE WHERE RN<>1;

2.Checking typing errors of category groups (level, subject)

SELECT DISTINCT [level]
FROM udemy_courses

SELECT DISTINCT [subject]
FROM udemy_courses;

image

---> There are 3 categorys type having typing error as 'Business Ffinance', 'Graphic Design', 'Musical Instrucmentss'

  • Update typing errors
UPDATE udemy_courses
SET    subject = REPLACE(subject,'Business Ffinance','Business Finance')

UPDATE udemy_courses
SET    subject = REPLACE(subject,'Graphic  Design','Graphic Design')

UPDATE udemy_courses
SET    subject = REPLACE(subject,'Musical Instrumentss','Musical Instruments')

3. Replace Null Values

UPDATE udemy_courses
SET is_paid = 'FALSE'
WHERE is_paid is NULL

4. Add one more column as Date as save file csv as "Results_Final1.csv"

SELECT *, CONVERT(VARCHAR(10), published_timestamp, 114) AS Date
FROM udemy_courses
  • First 5 rows :
course_id course_title url is_paid price num_subscribers num_reviews num_lectures level content_duration published_timestamp subject Date
1070968 Ultimate Investment Banking Course. https://www.udemy.com/ultimate-investment-banking-course/ TRUE 200 2147 23 51 All Levels 1.5 1/19/2017 3:58 Business Finance 1/18/2017
1113822 Complete GST Course & Certification - Grow Your CA Practice https://www.udemy.com/goods-and-services-tax/ TRUE 75 2792 923 274 All Levels 39 3/9/2017 23:34 Business Finance 3/9/2017
1006314 Financial Modeling for Business Analysts and Consultants https://www.udemy.com/financial-modeling-for-business-analysts-and-consultants/ TRUE 45 2174 74 51 Intermediate Level 2.5 12/20/2016 2:26 Business Finance 12/20/2016
1210588 Beginner to Pro - Financial Analysis in Excel 2017 https://www.udemy.com/complete-excel-finance-course-from-beginner-to-pro/ TRUE 95 2451 11 36 All Levels 3 5/31/2017 3:07 Business Finance 5/31/2017
1011058 How To Maximize Your Profits Trading Options https://www.udemy.com/how-to-maximize-your-profits-trading-options/ TRUE 200 1276 45 26 Intermediate Level 2 12/13/2016 21:57 Business Finance 12/13/2016
192870 Trading Penny Stocks: A Guide for All Levels In 2017 https://www.udemy.com/trading-penny-stocks-a-guide-for-all-levels/ TRUE 150 9221 138 25 All Levels 3 5/2/2014 22:13 Business Finance 5/2/2014

IMPORT CLEAN FILE TO POWER BI

1. Transform Data : Use First rows as Header, Change type of Is_paid to text data type, replace value "True" to "Paid" & "False" to "Free".

  • Source data : image
  • Promoted header, Change type & Replace value : image

2. Add one more column Total_Income = Price * num_subscribers

image

3.Add new measure dax - To calculate income different between quarter ?

image