Tag Archives: unused

How to identify and remove unused tables in SQL Server with T-Sql

In a perfect world an organisation should never get itself into the situation where tables need to be identified as functionally obsolete and removed in bulk. Schema changes should be stepped through the cycle of development, test, staging and live with developers cleaning as they go, but we don’t live in a perfect world as you may have noticed.

What do I mean by functionally obsolete? This means the tables are no longer being interacted with by user generated objects like stored procedures, functions or views. There may also be tables that could be classified as business redundant. That is they are being referenced by user generated objects frequently but they no longer have a use to the business, i.e. one job may have been replaced by another without the former being disabled or dropped. Business redundant objects are more difficult to determine and finding them may require input from multiple stakeholders.

A good approach for removing objects is to rename the objects first. This makes it easier to put the environment back the way it was if there are any problems encountered. After a set period of time if there is no impact on the overall environment script out the object then drop it. (Obviously do this in a test environment first if possible)

The script below is mostly a light weight SELECT statement that can be run on any environment. It does not execute any of the code it generates. It uses the sys.dm_db_index_usage_stats dynamic management view to determine when the tables were last interacted with. Interaction being defined as the following actions being applied against the object, update, seek, scan, lookup.

Caveat: Entries in this view reset to NULL after a Server reboot. Also the DMV has been known to be a bit unreliable with earlier versions of SQL Server with cases of the view being reset when a full index rebuild is carried out against a table. So don’t execute any code without first reviewing it.

Tables with NULL values for the fields below should be tables that have not been referenced at all or at least since the last time the server was rebooted.

LastUserUpdate
LastUserSeek
LastUserScan
LastUserLookup

Removing these objects is the low hanging fruit of cleaning up an environment. The script also provides stats on how many times these interactions happened and the size of the object. All these stats together should help you determine if an object is functionally redundant or business redundant and can be removed.

To aid further in the cleanup the script also creates the fields Action, Comments, Renamed, RenamedDate, RenameForDeletion, RestoreOriginalName, DropTable, DroppedDate.

The script output can then be copied and pasted into an Excel spread sheet and used to coordinate and track the cleanup progress.

SET NOCOUNT ON

DECLARE @Database TABLE ([DbName] [sysname])
DECLARE @DbName AS [sysname]
DECLARE @Sql AS [varchar] (max)

IF OBJECT_ID('tempdb..#TableStats', 'U') IS NOT NULL
	DROP TABLE #TableStats

IF OBJECT_ID('tempdb..#IndexStats', 'U') IS NOT NULL
	DROP TABLE #IndexStats

IF OBJECT_ID('tempdb..#TableUsageStats', 'U') IS NOT NULL
	DROP TABLE #TableUsageStats

IF OBJECT_ID('tempdb..#TableSizeStats', 'U') IS NOT NULL
	DROP TABLE #TableSizeStats

CREATE TABLE #TableStats (
	[DbName] [sysname]
	,[SchemaName] [sysname]
	,[ObjectId] [bigint]
	,[TableName] [sysname]
	,[ModifiedDate] [datetime]
	);

CREATE TABLE #IndexStats (
	[DbName] [sysname]
	,[ObjectId] [bigint]
	,[HasIndex] [bit]
	);

CREATE TABLE #TableSizeStats (
	[DbName] [varchar](255) NULL
	,[SchemaName] [varchar](255) NULL
	,[ObjectId] [bigint]
	,[TableName] [varchar](255) NULL
	,[RowCount] [bigint] NULL
	,[AvailableSpacePercentage] [numeric](6, 2) NULL
	,[UnusedSpaceGb] [numeric](10, 3) NULL
	,[UsedSpaceGb] [numeric](10, 3) NULL
	,[TotalSpaceGb] [numeric](10, 3) NULL
	,[UnusedSpaceMb] [numeric](13, 3) NULL
	,[UsedSpaceMb] [numeric](13, 3) NULL
	,[TotalSpaceMb] [numeric](13, 3) NULL
	,[UnusedSpaceKb] [bigint] NULL
	,[UsedSpaceKb] [bigint] NULL
	,[TotalSpaceKb] [bigint] NULL
	)

CREATE TABLE #TableUsageStats (
	[DbName] [sysname]
	,[ObjectId] [bigint]
	,[TableName] [nvarchar](128) NULL
	,[LastUserUpdate] [datetime] NULL
	,[LastUserSeek] [datetime] NULL
	,[LastUserScan] [datetime] NULL
	,[LastUserLookup] [datetime] NULL
	,[UserUpdateCount] [bigint] NOT NULL
	,[UserSeekCount] [bigint] NOT NULL
	,[UserScanCount] [bigint] NOT NULL
	,[UserLookupCount] [bigint] NOT NULL
	);

SET @DbName = '';

INSERT INTO @Database (DbName)
SELECT NAME
FROM master.dbo.sysdatabases
WHERE NAME NOT IN (
		'tempdb'
		,'master'
		,'mode'
		,'model'
		)
ORDER BY NAME ASC;

WHILE @DbName IS NOT NULL
BEGIN
	SET @DbName = (
			SELECT MIN(DbName)
			FROM @Database
			WHERE DbName > @DbName
			);
	SET @Sql = '
INSERT INTO #TableStats (
	DbName
	,schemaName
	,ObjectId
	,TableName
	,ModifiedDate
	)
SELECT DbName
	,SchemaName
	,ObjectId
	,TableName
	,ModifiedDate
FROM (
SELECT DISTINCT ' + '''' + @DbName + '''' + ' AS DbName
	,s.NAME AS SchemaName
	,t.object_id AS ObjectId
	,t.NAME AS TableName
	,t.modify_date AS ModifiedDate
FROM ' + QUOTENAME(@DbName) + '.sys.tables AS t
INNER JOIN ' + QUOTENAME(@DbName) + '.sys.schemas AS s ON t.schema_id = s.schema_id
LEFT JOIN ' + QUOTENAME(@DbName) + '.sys.extended_properties AS ep ON ep.major_id = t.[object_id] /*Exclude System Tables*/
WHERE t.NAME IS NOT NULL
	AND s.NAME IS NOT NULL
	AND (ep.[name] IS NULL OR ep.[name] <> ''microsoft_database_tools_support'')
	) AS rd
WHERE rd.SchemaName IS NOT NULL
ORDER BY DbName ASC
	,TableName ASC;
'

	EXEC (@Sql)

	SELECT @Sql = '
INSERT INTO #IndexStats (
	DbName
	,ObjectId
	,HasIndex
	)
SELECT ' + '''' + @DbName + '''' + ' AS DbName
	,OBJECT_ID AS ObjectId
	,IndexCheck AS HasIndex
FROM (
	SELECT DISTINCT OBJECT_ID
		,CASE 
			WHEN (
					[TYPE] > 0
					AND is_disabled = 0
					)
				THEN 1
			ELSE 0
			END AS IndexCheck
	FROM ' + QUOTENAME(@DbName) + '.sys.indexes
	) AS rd
WHERE rd.IndexCheck = 1
'

	EXEC (@Sql)

	SET @Sql = 
		'
INSERT INTO #TableSizeStats (
	[DbName]
	,[SchemaName]
	,[ObjectId]
	,[TableName]
	,[RowCount]
	,[AvailableSpacePercentage]
	,[UnusedSpaceGb]
	,[UsedSpaceGb]
	,[TotalSpaceGb]
	,[UnusedSpaceMb]
	,[UsedSpaceMb]
	,[TotalSpaceMb]
	,[UnusedSpaceKb]
	,[UsedSpaceKb]
	,[TotalSpaceKb]
	)
SELECT DISTINCT rd.[DbName]
	,rd.[SchemaName]
	,rd.[ObjectId]
	,rd.[TableName]
	,rd.[RowCount]
	,CASE 
		WHEN TotalSpaceKb > 0
			THEN ((UnusedSpaceKb / TotalSpaceKb) * 100)
		ELSE 0
		END AS AvailableSpacePercentage
	,CONVERT(NUMERIC(10, 3), (rd.[UnusedSpaceKb] / 1024.) / 1024.) AS UnusedSpaceGb
	,CONVERT(NUMERIC(10, 3), (rd.[UsedSpaceKb] / 1024.) / 1024.) AS UsedSpaceGb
	,CONVERT(NUMERIC(10, 3), (rd.[TotalSpaceKb] / 1024.) / 1024.) AS TotalSpaceGb
	,CONVERT(NUMERIC(13, 3), (rd.[UnusedSpaceKb] / 1024.)) AS UnusedSpaceMb
	,CONVERT(NUMERIC(13, 3), (rd.[UsedSpaceKb] / 1024.)) AS UsedSpaceMb
	,CONVERT(NUMERIC(13, 3), (rd.[TotalSpaceKb] / 1024.)) AS TotalSpaceMb
	,rd.[UnusedSpaceKb]
	,rd.[UsedSpaceKb]
	,rd.[TotalSpaceKb]
FROM (
	SELECT ' 
		+ '''' + @DbName + '''' + ' AS DbName
		,t.Object_id AS ObjectId
		,s.[name] AS [SchemaName]
		,t.[name] AS [TableName]
		,p.[rows] AS [RowCount]
		,SUM(a.[used_pages]) * 8 AS [UsedSpaceKb]
		,(SUM(a.[total_pages]) - SUM(a.[used_pages])) * 8 AS [UnusedSpaceKb]
		,SUM(a.[total_pages]) * 8 AS [TotalSpaceKb]
	FROM ' + QUOTENAME(@DbName) + '.sys.tables AS t
	INNER JOIN ' + QUOTENAME(@DbName) + '.sys.schemas AS s ON t.schema_id = s.schema_id
	INNER JOIN ' + QUOTENAME(@DbName) + '.sys.indexes AS i ON t.OBJECT_ID = i.object_id
	INNER JOIN ' + QUOTENAME(@DbName) + '.sys.partitions AS p ON i.object_id = p.OBJECT_ID
		AND i.[index_id] = p.[index_id]
	INNER JOIN ' + QUOTENAME(@DbName) + '.sys.allocation_units a ON p.[partition_id] = a.[container_id]
	WHERE t.[is_ms_shipped] = 0
		AND i.OBJECT_ID > 255
	GROUP BY s.[name]
		,t.[name]
		,t.[object_id]
		,p.[rows]
	) AS rd
ORDER BY DbName ASC
	,SchemaName ASC
	,TableName ASC;
'

	EXEC (@Sql)

	SET @Sql = '
INSERT INTO #TableUsageStats (
	[DbName]
	,[ObjectId]
	,[TableName]
	,[LastUserUpdate]
	,[LastUserSeek]
	,[LastUserScan]
	,[LastUserLookup]
	,[UserUpdateCount]
	,[UserSeekCount]
	,[UserScanCount]
	,[UserLookupCount]
	)
SELECT DbName
	,ObjectId
	,TableName
	,LastUserUpdate
	,LastUserSeek
	,LastUserScan
	,LastUserLookup
	,UserUpdateCount
	,UserSeekCount
	,UserScanCount
	,UserLookupCount
FROM (
	SELECT DISTINCT ROW_NUMBER() OVER (
			PARTITION BY ius.Object_Id ORDER BY last_user_update DESC
			) AS RN
		,' + '''' + @DbName + '''' + ' AS DbName
		,ius.OBJECT_ID AS ObjectId
		,o.NAME AS TableName
		,ius.last_user_update AS LastUserUpdate
		,ius.last_user_seek AS LastUserSeek
		,ius.last_user_scan AS LastUserScan
		,ius.last_user_lookup AS LastUserLookup
		,ius.user_updates AS UserUpdateCount
		,ius.user_seeks AS UserSeekCount
		,ius.user_scans AS UserScanCount
		,ius.user_lookups AS UserLookupCount
	FROM ' + QUOTENAME(@DbName) + 
		'.sys.dm_db_index_usage_stats AS ius
	INNER JOIN ' + QUOTENAME(@DbName) + '.sys.objects AS o ON ius.OBJECT_ID = o.OBJECT_ID
		AND o.NAME IS NOT NULL
	) AS rd
WHERE rd.RN = 1
ORDER BY rd.DbName ASC
	,rd.TableName ASC
	,rd.LastUserUpdate DESC
	,rd.LastUserSeek DESC
	,rd.LastUserScan DESC
	,rd.LastUserLookup DESC;
'

	EXEC (@Sql)
END;
GO

SELECT DISTINCT ROW_NUMBER() OVER (
		ORDER BY ts.[DbName] ASC
			,ts.[SchemaName] ASC
			,ts.[TableName] ASC
		) AS Row
	,ts.[DbName]
	,ts.[SchemaName]
	,ts.[TableName]
	,'' AS Action --Rename, keep etc.
	,'' AS Comments
	,'' AS Renamed --boolean flag
	,'' AS RenamedDate 
	,i.[HasIndex] --Tables without an index are heaps
	,tss.[TotalSpaceMb] AS TableSizeInMb
	,ts.[ModifiedDate]
	,tus.[LastUserUpdate]
	,tus.[LastUserSeek]
	,tus.[LastUserScan]
	,tus.[LastUserLookup]
	,tus.[UserUpdateCount]
	,tus.[UserSeekCount]
	,tus.[UserScanCount]
	,tus.[UserLookupCount]
	,tss.[AvailableSpacePercentage]
	,tss.[UnusedSpaceGb]
	,tss.[UsedSpaceGb]
	,tss.[TotalSpaceGb]
	,tss.[UnusedSpaceMb]
	,tss.[UsedSpaceMb]
	,tss.[TotalSpaceMb]
	,tss.[UnusedSpaceKb]
	,tss.[UsedSpaceKb]
	,tss.[TotalSpaceKb]
	,'USE ' + QUOTENAME(ts.[DbName]) + '; EXEC sp_rename ' + '''' + ts.[SchemaName] + '.' + ts.[TableName] + '''' + ', ' + '''' + '_DELETE_' + ts.[TableName] + '''' + ';' AS RenameForDeletion
	,'USE ' + QUOTENAME(ts.[DbName]) + '; EXEC sp_rename ' + '''' + ts.[SchemaName] + '.' + '_DELETE_' + ts.[TableName] + '''' + ', ' + '''' + ts.[TableName] + '''' + ';' AS RestoreOriginalName
	,'USE ' + QUOTENAME(ts.[DbName]) + '; DROP TABLE ' + QUOTENAME(ts.[SchemaName]) + '.' + '[' + '_DELETE_' + ts.[TableName] + ']' + ';' AS 'DropTable'
	,'' AS DroppedDate
FROM #TableStats AS ts
LEFT JOIN #TableSizeStats AS tss ON ts.ObjectId = tss.ObjectId
	AND tss.DbName = ts.DbName
LEFT JOIN #IndexStats AS i ON ts.ObjectId = i.ObjectId
	AND i.DbName = ts.DbName
LEFT JOIN #TableUsageStats AS tus ON ts.ObjectId = tus.ObjectId
	AND tus.DbName = ts.DbName
ORDER BY ts.[DbName] ASC
	,ts.[SchemaName] ASC
	,ts.[TableName] ASC

	-- REF: https://docs.microsoft.com/en-us/sql/relational-databases/system-dynamic-management-views/sys-dm-db-index-usage-stats-transact-sql