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Author: aaron-evans-cruz

SQL-Data-Cleaning.sql

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+/*
+Cleaning Data in SQL Queries
+*/
+
+SELECT *
+	FROM PortfolioProject..NashvilleHousing
+
+
+--------------------------------------------------
+
+-- Standardize Date Format
+
+SELECT SaleDate, 
+       CONVERT(Date, SaleDate)
+	FROM PortfolioProject..NashvilleHousing
+
+UPDATE NashvilleHousing
+	SET SaleDate = CONVERT(Date, SaleDate)
+
+-- If it doesn't Update properly
+
+ALTER TABLE NashvilleHousing
+	ADD SaleDateConverted Date
+
+UPDATE NashvilleHousing
+	SET SaleDateConverted = CONVERT(Date, SaleDate)
+
+-- Initially spelled the column name wrong that was adding as SaleDataConverted, so going to remove that column.
+
+ALTER TABLE NashvilleHousing
+	DROP COLUMN SaleDataConverted
+
+
+--------------------------------------------------
+
+-- Standardize Acreage
+
+SELECT Acreage,
+	   CAST(Acreage AS Decimal(5, 2))
+	   FROM PortfolioProject..NashvilleHousing
+
+UPDATE NashvilleHousing
+	SET Acreage = CAST(Acreage AS Decimal(5, 2))
+
+-- If it doesn't Update properly
+
+ALTER TABLE NashvilleHousing
+	ADD AcreageConverted Decimal(5,2)
+
+UPDATE NashvilleHousing
+	SET AcreageConverted = CAST(Acreage AS Decimal(5, 2))
+
+
+--------------------------------------------------
+
+-- Populate Property Address data
+
+SELECT *
+	FROM PortfolioProject..NashvilleHousing
+	--WHERE PropertyAddress is null
+	ORDER BY ParcelID
+
+SELECT a.ParcelID, 
+       a.PropertyAddress, 
+	   b.ParcelID, 
+	   b.PropertyAddress, 
+	   ISNULL(a.PropertyAddress,b.PropertyAddress)
+	FROM PortfolioProject..NashvilleHousing a
+	JOIN PortfolioProject..NashvilleHousing b
+	ON a.ParcelID = b.ParcelID
+	AND a.[UniqueID ] <> b.[UniqueID ]
+	WHERE a.PropertyAddress IS NULL
+
+UPDATE a
+	SET PropertyAddress = ISNULL(a.PropertyAddress,b.PropertyAddress)
+	FROM PortfolioProject..NashvilleHousing a
+	JOIN PortfolioProject..NashvilleHousing b
+	ON a.ParcelID = b.ParcelID
+	AND a.[UniqueID ] <> b.[UniqueID ]
+	WHERE a.PropertyAddress IS NULL
+
+
+--------------------------------------------------
+
+-- Breaking out Address into Individual Columns (Address, City, State)
+-- First up the Property Address, using Substrings
+
+SELECT PropertyAddress
+	FROM PortfolioProject..NashvilleHousing
+	--WHERE PropertyAddress is null
+	--ORDER BY ParcelID
+
+SELECT
+	SUBSTRING(PropertyAddress, 1, CHARINDEX(',', PropertyAddress) - 1) AS Address,
+	SUBSTRING(PropertyAddress, CHARINDEX(',', PropertyAddress) + 1, LEN(PropertyAddress)) AS City
+	FROM PortfolioProject..NashvilleHousing
+
+ALTER TABLE NashvilleHousing
+	ADD PropertySplitAddress nvarchar(255)
+
+UPDATE NashvilleHousing
+	SET PropertySplitAddress = SUBSTRING(PropertyAddress, 1, CHARINDEX(',', PropertyAddress) - 1)
+
+ALTER TABLE NashvilleHousing
+	ADD PropertySplitCity nvarchar(255)
+
+UPDATE NashvilleHousing
+	SET PropertySplitCity = SUBSTRING(PropertyAddress, CHARINDEX(',', PropertyAddress) + 1, LEN(PropertyAddress))
+
+SELECT *
+	FROM PortfolioProject..NashvilleHousing
+
+-- Next Up the Owner Address, using Parse Name instead of Substrings
+,
+SELECT OwnerAddress
+	FROM PortfolioProject..NashvilleHousing
+
+SELECT 
+	PARSENAME(REPLACE(OwnerAddress, ',', '.'), 3),
+	PARSENAME(REPLACE(OwnerAddress, ',', '.'), 2),
+	PARSENAME(REPLACE(OwnerAddress, ',', '.'), 1)
+	FROM PortfolioProject..NashvilleHousing
+
+ALTER TABLE NashvilleHousing
+	ADD OwnerSplitAddress nvarchar(255)
+
+UPDATE NashvilleHousing
+	SET OwnerSplitAddress = PARSENAME(REPLACE(OwnerAddress, ',', '.'), 3)
+
+ALTER TABLE NashvilleHousing
+	ADD OwnerSplitCity nvarchar(255)
+
+UPDATE NashvilleHousing
+	SET OwnerSplitCity = PARSENAME(REPLACE(OwnerAddress, ',', '.'), 2)
+
+ALTER TABLE NashvilleHousing
+	ADD OwnerSplitState nvarchar(255)
+
+UPDATE NashvilleHousing
+	SET OwnerSplitState = PARSENAME(REPLACE(OwnerAddress, ',', '.'), 1)
+
+SELECT *
+	FROM PortfolioProject..NashvilleHousing
+
+
+--------------------------------------------------
+
+-- Change Y and N to Yes and No in "Sold as Vacant" field
+
+SELECT DISTINCT(SoldAsVacant), 
+       COUNT(SoldAsVacant)
+	FROM PortfolioProject..NashvilleHousing
+	GROUP BY SoldAsVacant
+	ORDER BY 2
+
+SELECT SoldAsVacant,
+	CASE WHEN SoldAsVacant = 'Y' THEN 'YES'
+	     WHEN SoldAsVacant = 'N' THEN 'NO'
+	ELSE SoldAsVacant
+	END
+	FROM PortfolioProject..NashvilleHousing
+
+UPDATE NashvilleHousing
+	SET SoldAsVacant = 
+		CASE WHEN SoldAsVacant = 'Y' THEN 'YES'
+	    WHEN SoldAsVacant = 'N' THEN 'NO'
+	    ELSE SoldAsVacant
+	    END
+
+
+--------------------------------------------------
+
+-- Remove Duplicates - Not standard to remove data from a table, put practicing the action of.
+-- Using a CTE. Can't use Order By within one.
+
+WITH RowNumCTE AS (
+SELECT *, ROW_NUMBER() OVER (
+PARTITION BY ParcelID,
+			 PropertyAddress,
+			 SalePrice,
+			 SaleDate,
+			 LegalReference
+			 ORDER BY ParcelID 
+			 ) row_num
+FROM PortfolioProject..NashvilleHousing
+-- ORDER BY ParcelID
+)
+DELETE
+	FROM RowNumCTE
+	WHERE row_num > 1
+	--ORDER BY PropertyAddress
+
+
+--------------------------------------------------
+
+-- Delete Unused Columns. You don't do this to raw data that you put into your database.
+-- Again, just the practice of doing so.
+
+SELECT *
+	FROM PortfolioProject..NashvilleHousing
+
+ALTER TABLE PortfolioProject..NashvilleHousing
+DROP COLUMN PropertyAddress, TaxDistrict, OwnerAddress, SaleDate
+
+ALTER TABLE PortfolioProject..NashvilleHousing
+DROP COLUMN Acreage