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Data_Cleaning_Project_Company_Layoffs.sql

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+-- Data Cleaning Project
+
+SELECT *
+FROM layoffs;
+
+-- 1.Remove Duplicates 
+-- 2.Standardize the Data
+-- 3.Null Values or Blank Values
+-- 4. Remove Any un needed columns
+
+
+CREATE TABLE layoffs_staging
+LIKE layoffs;
+
+SELECT *
+FROM layoffs_staging;
+
+INSERT layoffs_staging
+SELECT *
+FROM layoffs;
+
+
+-- removing duplicates
+ SELECT *, 
+ ROW_NUMBER() OVER(
+ PARTITION BY company, industry, total_laid_off, percentage_laid_off, `date`) AS row_num
+FROM layoffs_staging;
+
+WITH duplicate_cte AS
+(
+ SELECT *, 
+ ROW_NUMBER() OVER(
+ PARTITION BY company, location,
+ industry, total_laid_off, percentage_laid_off, `date`, stage, 
+ country, funds_raised_millions) AS row_num
+FROM layoffs_staging
+)
+SELECT *
+FROM duplicate_cte
+WHERE row_num > 1;
+
+
+SELECT *
+FROM layoffs_staging
+WHERE company = 'Casper';
+
+
+WITH duplicate_cte AS
+(
+ SELECT *, 
+ ROW_NUMBER() OVER(
+ PARTITION BY company, location,
+ industry, total_laid_off, percentage_laid_off, `date`, stage, 
+ country, funds_raised_millions) AS row_num
+FROM layoffs_staging
+)
+SELECT *
+FROM duplicate_cte
+WHERE row_num > 1;
+
+
+CREATE TABLE `layoffs_staging2` (
+  `company` text,
+  `location` text,
+  `industry` text,
+  `total_laid_off` int DEFAULT NULL,
+  `percentage_laid_off` text,
+  `date` text,
+  `stage` text,
+  `country` text,
+  `funds_raised_millions` int DEFAULT NULL,
+  `row_num` INT
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci;
+
+
+
+
+SELECT *
+FROM layoffs_staging2;
+
+INSERT INTO layoffs_staging2
+ SELECT *, 
+ ROW_NUMBER() OVER(
+ PARTITION BY company, location,
+ industry, total_laid_off, percentage_laid_off, `date`, stage, 
+ country, funds_raised_millions) AS row_num
+FROM layoffs_staging;
+
+
+SELECT *
+FROM layoffs_staging2
+WHERE row_num > 1
+;
+
+DELETE
+FROM layoffs_staging2
+WHERE row_num > 1
+;
+
+SELECT *
+FROM layoffs_staging2
+WHERE row_num > 1
+;
+
+SELECT *
+FROM layoffs_staging2;
+
+-- standardizing data
+
+-- Check each column for potential issues
+
+-- Remove unnecessary space from company names
+SELECT company, (TRIM(company))
+FROM layoffs_staging2;
+
+UPDATE layoffs_staging2
+SET company = TRIM(company);
+
+
+
+SELECT DISTINCT industry
+FROM layoffs_staging2
+ORDER BY 1
+;
+
+-- Need to update following industries as they're essentially the same
+# industry
+'Crypto'
+'Crypto Currency'
+'CryptoCurrency'
+
+SELECT *
+FROM layoffs_staging2
+WHERE industry LIKE '%Crypto%'
+;
+
+UPDATE layoffs_staging2
+SET industry = 'Crypto'
+WHERE industry LIKE '%Crypto%'
+;
+
+SELECT DISTINCT industry
+FROM layoffs_staging2
+;
+
+SELECT DISTINCT location
+FROM layoffs_staging2
+ORDER BY 1
+;
+-- Everything seems ok in location column
+
+SELECT DISTINCT country
+FROM layoffs_staging2
+ORDER BY 1
+;
+
+-- Issue found United States with and without a full stop / period.
+# country
+'United States'
+'United States.'
+
+-- First check to see which one os the correct version
+SELECT *
+FROM layoffs_staging2
+WHERE country LIKE 'United States%'
+ORDER BY 1
+;
+
+-- without full stop is correct version
+
+
+SELECT DISTINCT country, TRIM(TRAILING '.' FROM country) Trimmed_country
+FROM layoffs_staging2
+ORDER BY 1;
+
+UPDATE layoffs_staging2
+SET country = TRIM(TRAILING '.' FROM country)
+WHERE country LIKE 'United States%'
+;
+
+
+SELECT *
+FROM layoffs_staging2
+;
+
+-- Data type for date is currently set as Text need to change it.
+SELECT `date`,
+STR_TO_DATE(`date`, '%m/%d/%Y')
+FROM layoffs_staging2;
+
+UPDATE layoffs_staging2
+SET `date` = STR_TO_DATE(`date`, '%m/%d/%Y');
+
+SELECT `date`
+FROM layoffs_staging2;
+
+-- Now we can alter the date data type 
+ALTER TABLE layoffs_staging2
+MODIFY COLUMN `date` DATE;
+
+-- Populate null values
+
+SELECT *
+FROM layoffs_staging2
+WHERE total_laid_off IS NULL
+AND percentage_laid_ofF IS NULL
+;
+
+SELECT *
+FROM layoffs_staging2
+WHERE industry IS NULL
+
+;
+
+
+
+SELECT *
+FROM layoffs_staging2
+WHERE industry IS NULL
+OR industry = '';
+
+-- Check if other rows are populated 
+SELECT *
+FROM layoffs_staging2
+WHERE company = 'Airbnb';
+
+# company, location, industry, total_laid_off, percentage_laid_off, date, stage, country, funds_raised_millions, row_num
+'Airbnb', 'SF Bay Area', '', '30', NULL, '2023-03-03', 'Post-IPO', 'United States', '6400', '1'
+'Airbnb', 'SF Bay Area', 'Travel', '1900', '0.25', '2020-05-05', 'Private Equity', 'United States', '5400', '1'
+
+-- Found company column populated industry as 'Travel' we can now fill the empty space
+
+-- Check what other companies have some rows with empty industries and some populated.
+
+SELECT *
+FROM layoffs_staging2 t1
+JOIN layoffs_staging2 t2
+	ON t1.company = t2.company
+    AND t1.location = t2.location
+WHERE (t1.industry IS NULL OR t1.industry = '')
+AND t2.industry IS NOT NULL
+;
+
+-- Transalatethe above to an update statement.
+
+UPDATE layoffs_staging2 t1
+JOIN layoffs_staging2 t2
+	ON t1.company = t2.company
+SET t1.industry = t2.industry
+WHERE (t1.industry IS NULL OR t1.industry = '')
+AND t2.industry IS NOT NULL
+;
+
+SELECT t1.industry, t2.industry
+FROM layoffs_staging2 t1
+JOIN layoffs_staging2 t2
+	ON t1.company = t2.company
+    AND t1.location = t2.location
+WHERE (t1.industry IS NULL OR t1.industry = '')
+AND t2.industry IS NOT NULL
+;
+
+-- UPDATE didnt work possibly because its ' ' and not null. next step set empty space to null.
+
+
+UPDATE layoffs_staging2
+SET industry = null
+WHERE industry = '';
+
+-- Retry update query 
+
+UPDATE layoffs_staging2 t1
+JOIN layoffs_staging2 t2
+	ON t1.company = t2.company
+SET t1.industry = t2.industry
+WHERE (t1.industry IS NULL OR t1.industry = '')
+AND t2.industry IS NOT NULL
+;
+
+SELECT *
+FROM layoffs_staging2
+WHERE company = 'Airbnb';
+
+-- works great now
+
+
+SELECT *
+FROM layoffs_staging2
+WHERE industry IS NULL
+OR industry = '';
+
+# company, location, industry, total_laid_off, percentage_laid_off, date, stage, country, funds_raised_millions, row_num
+'Bally\'s Interactive', 'Providence', NULL, NULL, '0.15', '2023-01-18', 'Post-IPO', 'United States', '946', '1'
+-- this one is still null
+
+SELECT *
+FROM layoffs_staging2
+WHERE company LIKE 'Bally%';
+
+-- There only one row. Others had other rows (lay offs)
+
+-- Removing un needed column and rows.
+
+SELECT *
+FROM layoffs_staging2
+WHERE total_laid_off IS NULL
+AND percentage_laid_ofF IS NULL
+;
+
+
+DELETE
+FROM layoffs_staging2
+WHERE total_laid_off IS NULL
+AND percentage_laid_ofF IS NULL
+;
+
+SELECT *
+FROM layoffs_staging2;
+
+ALTER TABLE layoffs_staging2
+DROP COLUMN row_num;
+
+-- Data is now CLEAN!
+