Data Cleaning Queries.sql

/*

Cleaning Data in SQL Queries

*/


Select *
From PortfolioProject.dbo.NashvilleHousing

--------------------------------------------------------------------------------------------------------------------------

-- Standardize Date Format

Select SaleDate, CONVERT (Date,SaleDate)
From PortfolioProject.dbo.NashvilleHousing


Update NashvilleHousing
SET SaleDate = CONVERT(Date,SaleDate)

Update NashvilleHousing
SET SaleDateConverted = CONVERT(Date,SaleDate)

Select SaleDateConverted, CONVERT(Date,SaleDate)
From PortfolioProject.dbo.NashvilleHousing

 --------------------------------------------------------------------------------------------------------------------------

-- Populate Property Address data

 --Where Property Address is NULL
Select *
From PortfolioProject.dbo.NashvilleHousing
Where PropertyAddress is null

--Order by Parcel ID
Select *
From PortfolioProject.dbo.NashvilleHousing
order by ParcelID

--Distinguish Unique ID
Select*
From PortfolioProject.dbo.NashvilleHousing a
JOIN PortfolioProject.dbo.NashvilleHousing b
     on a.ParcelID = b.ParcelID
	 AND a.[UniqueID ] <> b.[UniqueID ]

--Populate property Address
Select a.ParcelID, a.PropertyAddress, b.ParcelID, b.PropertyAddress, ISNULL(a.PropertyAddress,b.PropertyAddress)
From PortfolioProject.dbo.NashvilleHousing a
JOIN PortfolioProject.dbo.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.dbo.NashvilleHousing a
JOIN PortfolioProject.dbo.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)


Select PropertyAddress
From PortfolioProject.dbo.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 Address

From PortfolioProject.dbo.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.dbo.NashvilleHousing





Select OwnerAddress
From PortfolioProject.dbo.NashvilleHousing


Select
PARSENAME(REPLACE(OwnerAddress, ',', '.') , 3)
,PARSENAME(REPLACE(OwnerAddress, ',', '.') , 2)
,PARSENAME(REPLACE(OwnerAddress, ',', '.') , 1)
From PortfolioProject.dbo.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.dbo.NashvilleHousing




--------------------------------------------------------------------------------------------------------------------------


-- Change Y and N to Yes and No in "Sold as Vacant" field


Select Distinct(SoldAsVacant), Count(SoldAsVacant)
From PortfolioProject.dbo.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.dbo.NashvilleHousing


Update NashvilleHousing
SET SoldAsVacant = CASE When SoldAsVacant = 'Y' THEN 'Yes'
	   When SoldAsVacant = 'N' THEN 'No'
	   ELSE SoldAsVacant
	   END


Select Distinct(SoldAsVacant), Count(SoldAsVacant)
From PortfolioProject.dbo.NashvilleHousing
Group by SoldAsVacant
order by 2



-----------------------------------------------------------------------------------------------------------------------------------------------------------

-- Remove Duplicates

--Viewing duplicates
Select *,
	ROW_NUMBER() OVER (
	PARTITION BY ParcelID,
				 PropertyAddress,
				 SalePrice,
				 SaleDate,
				 LegalReference
				 ORDER BY
					UniqueID
					) row_num

From PortfolioProject.dbo.NashvilleHousing
Order by ParcelID

--Delete duplicates
WITH RowNumCTE AS(
Select *,
	ROW_NUMBER() OVER (
	PARTITION BY ParcelID,
				 PropertyAddress,
				 SalePrice,
				 SaleDate,
				 LegalReference
				 ORDER BY
					UniqueID
					) row_num

From PortfolioProject.dbo.NashvilleHousing
--order by ParcelID
)
DELETE
From RowNumCTE
Where row_num > 1


--Confirm whether duplicates still exist
WITH RowNumCTE AS(
Select *,
	ROW_NUMBER() OVER (
	PARTITION BY ParcelID,
				 PropertyAddress,
				 SalePrice,
				 SaleDate,
				 LegalReference
				 ORDER BY
					UniqueID
					) row_num

From PortfolioProject.dbo.NashvilleHousing
--order by ParcelID
)
Select *
From RowNumCTE
Where row_num > 1
Order by PropertyAddress


---Check data for duplicates
Select *
From PortfolioProject.dbo.NashvilleHousing




---------------------------------------------------------------------------------------------------------

-- Delete Unused Columns



Select *
From PortfolioProject.dbo.NashvilleHousing


ALTER TABLE PortfolioProject.dbo.NashvilleHousing
DROP COLUMN OwnerAddress, TaxDistrict, PropertyAddress, SaleDate


Select *
From PortfolioProject.dbo.NashvilleHousing