functions/Find-DbaUnusedIndex.ps1

function Find-DbaUnusedIndex {
    <#
        .SYNOPSIS
            Find Unused indexes
 
        .DESCRIPTION
            This command will help you to find Unused indexes on a database or a list of databases
 
            Also tells how much space you can save by dropping the index.
            We show the type of compression so you can make a more considered decision.
            For now only supported for CLUSTERED and NONCLUSTERED indexes
 
            You can select the indexes you want to drop on the gridview and by clicking OK the drop statement will be generated.
 
        .PARAMETER SqlInstance
            The SQL Server you want to check for unused indexes.
         
        .PARAMETER SqlCredential
             Allows you to login to servers using SQL Logins instead of Windows Authentication (AKA Integrated or Trusted). To use:
 
            $cred = Get-Credential, then pass $cred object to the -SqlCredential parameter.
 
            Windows Authentication will be used if SqlCredential is not specified. SQL Server does not accept Windows credentials being passed as credentials.
 
            To connect as a different Windows user, run PowerShell as that user.
 
        .PARAMETER Database
            The database(s) to process. Options for this list are auto-populated from the server. If unspecified, all databases will be processed.
 
        .PARAMETER ExcludeDatabase
            Specifies the database(s) to exclude from processing. Options for this list are auto-populated from the server.
 
        .PARAMETER FilePath
            Specifies the path of a file to write the DROP statements to.
 
        .PARAMETER NoClobber
            If this switch is enabled, the output file will not be overwritten.
             
        .PARAMETER Append
            If this switch is enabled, content will be appended to the output file.
 
        .PARAMETER WhatIf
            If this switch is enabled, no actions are performed but informational messages will be displayed that explain what would happen if the command were to run.
 
        .PARAMETER Confirm
            If this switch is enabled, you will be prompted for confirmation before executing any operations that change state.
 
        .PARAMETER Silent
            If this switch is enabled, the internal messaging functions will be silenced.
 
        .NOTES
            Tags: Indexes
            Author: Aaron Nelson (@SQLvariant), SQLvariant.com
 
            Website: https://dbatools.io
            Copyright: (C) Chrissy LeMaire, clemaire@gmail.com
            License: GNU GPL v3 https://opensource.org/licenses/GPL-3.0
 
        .LINK
            https://dbatools.io/Find-DbaUnusedIndex
 
        .EXAMPLE
            Find-DbaUnusedIndex -SqlInstance sql2005 -FilePath C:\temp\sql2005-UnusedIndexes.sql
 
            Generates the SQL statements to drop the selected unused indexes on server "sql2005". The statements are written to the file "C:\temp\sql2005-UnusedIndexes.sql"
 
        .EXAMPLE
            Find-DbaUnusedIndex -SqlInstance sql2005 -FilePath C:\temp\sql2005-UnusedIndexes.sql -Append
 
            Generates the SQL statements to drop the selected unused indexes on server "sql2005". The statements are written to the file "C:\temp\sql2005-UnusedIndexes.sql", appending if the file already exists.
 
        .EXAMPLE
            Find-DbaUnusedIndex -SqlInstance sqlserver2016 -SqlCredential $cred
 
            Generates the SQL statements to drop the selected unused indexes on server "sqlserver2016", using SQL Authentication to connect to the database.
 
        .EXAMPLE
            Find-DbaUnusedIndex -SqlInstance sqlserver2016 -Database db1, db2
 
            Generates the SQL Statement to to drop selected indexes in databases db1 & db2 on server "sqlserver2016".
 
        .EXAMPLE
            Find-DbaUnusedIndex -SqlInstance sqlserver2016
 
            Generates the SQL statements to drop selected indexes on all user databases.
    #>

    [CmdletBinding(SupportsShouldProcess = $true)]
    Param (
        [parameter(Mandatory = $true, ValueFromPipeline = $true)]
        [Alias("ServerInstance", "SqlServer")]
        [DbaInstanceParameter[]]$SqlInstance,
        [PSCredential]
        $SqlCredential,
        [Alias("Databases")]
        [object[]]$Database,
        [object[]]$ExcludeDatabase,
        [Alias("OutFile", "Path")]
        [string]$FilePath,
        [switch]$NoClobber,
        [switch]$Append,
        [switch]$Silent
    )

    begin {

        # Support Compression 2008+
        $unusedQuery = "
        SELECT DB_NAME(database_id) AS 'DatabaseName', s.name AS 'SchemaName', t.name AS 'TableName', i.object_id , i.name AS 'IndexName', i.index_id, i.type_desc , user_seeks , user_scans , user_lookups , user_updates , last_user_seek , last_user_scan , last_user_lookup , last_user_UPDATE , system_seeks , system_scans , system_lookups , system_updates , last_system_seek , last_system_scan , last_system_lookup , last_system_update
        FROM SYS.TABLES T
        JOIN SYS.SCHEMAS S
            ON T.schema_id = s.schema_id
        JOIN SYS.indexes i
            ON i.object_id = t.object_id LEFT OUTER
        JOIN sys.dm_db_index_usage_stats iu
            ON iu.object_id = i.object_id
                AND iu.index_id = i.index_id
        WHERE iu.database_id = DB_ID()
                AND OBJECTPROPERTY(i.[object_id], 'IsMSShipped') = 0
                AND user_seeks = 0
                AND user_scans = 0
                AND user_lookups = 0
                AND i.type_desc NOT IN ('HEAP', 'CLUSTERED COLUMNSTORE')"


        if ($FilePath.Length -gt 0) {
            if ($FilePath -notlike "*\*") {
                $FilePath = ".\$FilePath"
            }
            $directory = Split-Path $FilePath
            $exists = Test-Path $directory

            if ($exists -eq $false) {
                Stop-Function -Message "Parent directory $directory does not exist."
                return
            }
        }

        Write-Message -Level Output -Message "Attempting to connect to Sql Server."
        $server = Connect-SqlInstance -SqlInstance $SqlInstance -SqlCredential $SqlCredential
    }
    process {
        if (Test-FunctionInterrupt) { return }

        if ($server.VersionMajor -lt 9) {
            Stop-Function -Message "This function does not support versions lower than SQL Server 2005 (v9)."
            return
        }

        $lastRestart = $server.Databases['tempdb'].CreateDate
        $endDate = Get-Date -Date $lastRestart
        $diffDays = (New-TimeSpan -Start $endDate -End (Get-Date)).Days

        if ($diffDays -le 6) {
            Stop-Function -Message "The SQL Service was restarted on $lastRestart, which is not long enough for a solid evaluation."
            return
        }

        <#
            Validate if server version is:
                - sql 2012 and if have SP3 CU3 (Build 6537) or higher
                - sql 2014 and if have SP2 (Build 5000) or higher
            If the major version is the same but the build is lower, throws the message
        #>

        if (
            ($server.VersionMajor -eq 11 -and $server.BuildNumber -lt 6537) `
                -or ($server.VersionMajor -eq 12 -and $server.BuildNumber -lt 5000)
        ) {
            Stop-Function -Message "This SQL version has a known issue. Rebuilding an index clears any existing row entry from sys.dm_db_index_usage_stats for that index.`r`nPlease refer to connect item: https://connect.microsoft.com/sqlserver/feedback/details/739566/rebuilding-an-index-clears-stats-from-sys-dm-db-index-usage-stats"
            return
        }

        if ($diffDays -le 33) {
            Write-Message -Level Warning -Message "The SQL Service was restarted on $lastRestart, which may not be long enough for a solid evaluation."
        }

        if ($pipedatabase.Length -gt 0) {
            $database = $pipedatabase.name
        }

        if ($database.Count -eq 0) {
            $database = ($server.Databases | Where-Object { $_.IsSystemObject -eq 0 -and $_.IsAccessible}).Name
        }

        if ($database.Count -gt 0) {
            foreach ($db in $database) {
                if ($ExcludeDatabase -contains $db -or $null -eq $server.Databases[$db]) {
                    continue
                }
                if ($server.Databases[$db].IsAccessible -eq $false) {
                    Write-Message -Level Warning -Message "Database [$db] is not accessible."
                    continue
                }
                try {
                    Write-Message -Level Output -Message "Getting indexes from database '$db'."

                    $sql = $unusedQuery

                    $unusedIndex = $server.Databases[$db].ExecuteWithResults($sql)

                    $scriptGenerated = $false

                    if ($unusedIndex.Tables[0].Rows.Count -gt 0) {
                        $indexesToDrop = $unusedIndex.Tables[0] | Out-GridView -Title "Unused Indexes on $($db) database - Choose indexes to generate DROP script" -PassThru

                        #When only 1 line selected, the count does not work
                        if ($indexesToDrop.Count -gt 0 -or !([string]::IsNullOrEmpty($indexesToDrop))) {
                            #reset to #Yes
                            $result = 0

                            if ($unusedIndex.Tables[0].Rows.Count -eq $indexesToDrop.Count) {
                                $title = "Indexes to drop on databases '$db':"
                                $message = "You will generate drop statements to all indexes.`r`nPerhaps you want to keep at least one.`r`nDo you wish to generate the script anyway? (Y/N)"
                                $yes = New-Object System.Management.Automation.Host.ChoiceDescription "&Yes", "Will continue"
                                $no = New-Object System.Management.Automation.Host.ChoiceDescription "&No", "Will exit"
                                $options = [System.Management.Automation.Host.ChoiceDescription[]]($yes, $no)
                                $result = $host.ui.PromptForChoice($title, $message, $options, 0)
                            }

                            #default OR answer = YES
                            if ($result -eq 0) {
                                $sqlout = "/*`r`n"
                                $sqlout += "`tScript generated @ $(Get-Date -format "yyyy-MM-dd HH:mm:ss.ms")`r`n"
                                $sqlout += "`tDatabase: $($db)`r`n"
                                $sqlout += "`tConfirm that you have chosen the right indexes before execute the drop script`r`n"
                                $sqlout += "*/`r`n"

                                foreach ($index in $indexesToDrop) {
                                    if ($FilePath.Length -gt 0) {
                                        Write-Message -Level Output -Message "Exporting $($index.TableName).$($index.IndexName)"
                                    }

                                    $sqlout += "USE [$($index.DatabaseName)]`r`n"
                                    $sqlout += "GO`r`n"
                                    $sqlout += "IF EXISTS (SELECT 1 FROM sys.indexes WHERE [object_id] = OBJECT_ID('$($index.SchemaName).$($index.TableName)') AND name = '$($index.IndexName)')`r`n"
                                    $sqlout += " DROP INDEX $($index.SchemaName).$($index.TableName).$($index.IndexName)`r`n"
                                    $sqlout += "GO`r`n`r`n"
                                }

                                if ($FilePath.Length -gt 0) {
                                    $sqlout | Out-File -FilePath $FilePath -Append:$Append -NoClobber:$NoClobber
                                }
                                else {
                                    $sqlout
                                }

                                $scriptGenerated = $true
                            }
                            #answer = no
                            else {
                                Write-Message -Level Warning -Message "Script will not be generated for database '$db'"
                            }
                        }
                    }
                    else {
                        Write-Message -Level Output -Message "No Unused indexes found!"
                    }
                }
                catch {
                    Stop-Function -Message "Issue gathering indexes" -Category InvalidOperation -InnerErrorRecord $_ -Target $db
                }
            }

            if ($scriptGenerated) {
                Write-Message -Level Warning -Message "Confirm the generated script before execute!"
            }
            if ($FilePath.Length -gt 0) {
                Write-Message -Level Output -Message "Script generated to $FilePath"
            }
        }
        else {
            Write-Message -Level Output -Message "There are no databases to analyse."
        }
    }
    end {
        if (Test-FunctionInterrupt) {
            return
        }
        Test-DbaDeprecation -DeprecatedOn "1.0.0" -Alias Get-SqlUnusedIndex
    }
}