Reset identity seed after deleting records in SQL Server

Question

I have inserted records into a SQL Server database table. The table had a primary key defined and the auto increment identity seed is set to “Yes”. This is done primarily because in SQL Azure, each table has to have a primary key and identity defined.

But since I have to delete some records from the table, the identity seed for those tables will be disturbed and the index column (which is auto-generated with an increment of 1) will get disturbed.

How can I reset the identity column after I deleted the records so that the column has sequence in ascending numerical order?

The identity column is not used as a foreign key anywhere in database.

Answer 1

The DBCC CHECKIDENT management command is used to reset identity counter. The command syntax is:

DBCC CHECKIDENT (table_name [, { NORESEED | { RESEED [, new_reseed_value ]}}])
[ WITH NO_INFOMSGS ]

Example:

DBCC CHECKIDENT ('[TestTable]', RESEED, 0);
GO

It was not supported in previous versions of the Azure SQL Database but is supported now.

---

Thanks to Solomon Rutzky the docs for the command are now fixed.

Answer 2

DBCC CHECKIDENT ('TestTable', RESEED, 0)
GO

Where 0 is identity Start value

Answer 3

Although most answers are suggesting RESEED to 0, many times we need to just reseed to next Id available

declare @max int
select @max=max([Id]) from [TestTable]
if @max IS NULL   --check when max is returned as null
  SET @max = 0
DBCC CHECKIDENT ('[TestTable]', RESEED, @max)

This will check the table and reset to the next ID.

Answer 4

It should be noted that IF all of the data is being removed from the table via the DELETE (ie no WHERE clause), then as long as a) permissions allow for it, and b) there are no FKs referencing the table (which appears to be the case here), using TRUNCATE TABLE would be preferred as it does a more efficient DELETE and resets the IDENTITY seed at the same time. The following details are taken from the MSDN page for TRUNCATE TABLE :

Compared to the DELETE statement, TRUNCATE TABLE has the following advantages:

• Less transaction log space is used.

  The DELETE statement removes rows one at a time and records an entry in the transaction log for each deleted row. TRUNCATE TABLE removes the data by deallocating the data pages used to store the table data and records only the page deallocations in the transaction log.

• Fewer locks are typically used.

  When the DELETE statement is executed using a row lock, each row in the table is locked for deletion. TRUNCATE TABLE always locks the table (including a schema (SCH-M) lock) and page but not each row.

• Without exception, zero pages are left in the table.

  After a DELETE statement is executed, the table can still contain empty pages. For example, empty pages in a heap cannot be deallocated without at least an exclusive (LCK_M_X) table lock. If the delete operation does not use a table lock, the table (heap) will contain many empty pages. For indexes, the delete operation can leave empty pages behind, although these pages will be deallocated quickly by a background cleanup process.

If the table contains an identity column, the counter for that column is reset to the seed value defined for the column. If no seed was defined, the default value 1 is used. To retain the identity counter, use DELETE instead.

So the following:

DELETE FROM [MyTable];
DBCC CHECKIDENT ('[MyTable]', RESEED, 0);

Becomes just:

TRUNCATE TABLE [MyTable];

Please see the TRUNCATE TABLE documentation (linked above) for additional information on restrictions, etc.

Answer 5

I tried @anil shahs answer and it reset the identity. But when a new row was inserted it got the identity = 2 . So instead I changed the syntax to:

DELETE FROM [TestTable]

DBCC CHECKIDENT ('[TestTable]', RESEED, 0)
GO

Then the first row will get the identity = 1.

Answer 6

Although most answers are suggesting RESEED to 0 , and while some see this as a flaw for TRUNCATED tables, Microsoft has a solution that excludes the ID

DBCC CHECKIDENT ('[TestTable]', RESEED)

This will check the table and reset to the next ID . This has been available since MS SQL 2005 to current.

https://msdn.microsoft.com/en-us/library/ms176057.aspx

Answer 7

issuing 2 command can do the trick

DBCC CHECKIDENT ('[TestTable]', RESEED,0)
DBCC CHECKIDENT ('[TestTable]', RESEED)

the first reset the identity to zero , and the next will set it to the next available value -- jacob

Answer 8

@jacob

DBCC CHECKIDENT ('[TestTable]', RESEED,0)
DBCC CHECKIDENT ('[TestTable]', RESEED)

Worked for me, I just had to clear all entries first from the table, then added the above in a trigger point after delete. Now whenever i delete an entry is taken from there.

Answer 9

Truncate table is preferred because it clears the records, resets the counter and reclaims the disk space.

Delete and CheckIdent should be used only where foreign keys prevent you from truncating.

Answer 10

Reset identity column with new id...

DECLARE @MAX INT
SELECT @MAX=ISNULL(MAX(Id),0) FROM [TestTable]

DBCC CHECKIDENT ('[TestTable]', RESEED,@MAX)

Answer 11

This is a common question and the answer is always the same: don't do it. Identity values should be treated as arbitrary and, as such, there is no "correct" order.

Answer 12

Run this script to reset the identity column. You will need to make two changes. Replace tableXYZ with whatever table you need to update. Also, the name of the identity column needs dropped from the temp table. This was instantaneous on a table with 35,000 rows & 3 columns. Obviously, backup the table and first try this in a test environment.

---

select * 
into #temp
From tableXYZ

set identity_insert tableXYZ ON

truncate table tableXYZ

alter table #temp drop column (nameOfIdentityColumn)

set identity_insert tableXYZ OFF

insert into tableXYZ
select * from #temp

Answer 13

I use the following script to do this. There's only one scenario in which it will produce an "error", which is if you have deleted all rows from the table, and IDENT_CURRENT is currently set to 1, ie there was only one row in the table to begin with.

DECLARE @maxID int = (SELECT MAX(ID) FROM dbo.Tbl)
;

IF @maxID IS NULL
    IF (SELECT IDENT_CURRENT('dbo.Tbl')) > 1
        DBCC CHECKIDENT ('dbo.Tbl', RESEED, 0)
    ELSE
        DBCC CHECKIDENT ('dbo.Tbl', RESEED, 1)
    ;
ELSE
    DBCC CHECKIDENT ('dbo.Tbl', RESEED, @maxID)
;

Answer 14

I've been trying to get this done for a large number of tables during development, and this works as a charm.

DBCC CHECKIDENT('www.newsType', RESEED, 1);
DBCC CHECKIDENT('www.newsType', RESEED);

So, you first force it to be set to 1, then you set it to the highest index of the rows present in the table. Quick and easy rest of the idex.

Answer 15

I have just used DBCC CHECKIDENT successfully

Things to note:

• when referencing table name square brackets are not accepted
• DBCC CHECKIDENT('TableName',RESEED,n) will reset back to n+1
  • eg DBCC CHECKIDENT('tablename',RESEED,27) will start at 28
• if you are having issues with not setting the new starting id - noting this you could fix this by:

    DECLARE @NewId as INT  
    SET @NewId =  (SELECT MAX('TableName')-1  AS ID FROM TableName)
    DBCC CHECKIDENT('TableName',RESEED,@MaxId)

Answer 16

DBCC CHECKIDENT (<TableName>, reseed, 0)

This will set the current identity value to 0.

On inserting the next value, the identity value get incremented to 1.

Answer 17

Use this stored procedure:

IF (object_id('[dbo].[pResetIdentityField]') IS NULL)
  BEGIN
    EXEC('CREATE PROCEDURE [dbo].[pResetIdentityField] AS SELECT 1 FROM DUMMY');
  END
GO

SET  ANSI_NULLS ON
GO
SET  QUOTED_IDENTIFIER ON
GO

ALTER PROCEDURE [dbo].[pResetIdentityField]
  @pSchemaName NVARCHAR(1000)
, @pTableName NVARCHAR(1000) AS
DECLARE @max   INT;
DECLARE @fullTableName   NVARCHAR(2000) = @pSchemaName + '.' + @pTableName;

DECLARE @identityColumn   NVARCHAR(1000);

SELECT @identityColumn = c.[name]
FROM sys.tables t
     INNER JOIN sys.schemas s ON t.[schema_id] = s.[schema_id]
     INNER JOIN sys.columns c ON c.[object_id] = t.[object_id]
WHERE     c.is_identity = 1
      AND t.name = @pTableName
      AND s.[name] = @pSchemaName

IF @identityColumn IS NULL
  BEGIN
    RAISERROR(
      'One of the following is true: 1. the table you specified doesn''t have an identity field, 2. you specified an invalid schema, 3. you specified an invalid table'
    , 16
    , 1);
    RETURN;
  END;

DECLARE @sqlString   NVARCHAR(MAX) = N'SELECT @maxOut = max(' + @identityColumn + ') FROM ' + @fullTableName;

EXECUTE sp_executesql @stmt = @sqlString, @params = N'@maxOut int OUTPUT', @maxOut = @max OUTPUT

IF @max IS NULL
  SET @max = 0

print(@max)

DBCC CHECKIDENT (@fullTableName, RESEED, @max)
go

--exec pResetIdentityField 'dbo', 'Table'

Just revisiting my answer. I came across a weird behaviour in sql server 2008 r2 that you should be aware of.

drop table test01

create table test01 (Id int identity(1,1), descr nvarchar(10))

execute pResetIdentityField 'dbo', 'test01'

insert into test01 (descr) values('Item 1')

select * from test01

delete from test01

execute pResetIdentityField 'dbo', 'test01'

insert into test01 (descr) values('Item 1')

select * from test01

The first select produces 0, Item 1 .

The second one produces 1, Item 1 . If you execute the reset right after the table is created the next value is 0. Honestly, I am not surprised Microsoft cannot get this stuff right. I discovered it because I have a script file that populates reference tables that I sometimes run after I re-create tables and sometimes when the tables are already created.

Answer 18

For a complete DELETE rows and reset the IDENTITY count, I use this (SQL Server 2008 R2)

USE mydb

-- ##################################################################################################################
-- DANGEROUS!!!! USE WITH CARE
-- ##################################################################################################################

DECLARE
  db_cursor CURSOR FOR
    SELECT TABLE_NAME
      FROM INFORMATION_SCHEMA.TABLES
     WHERE TABLE_TYPE = 'BASE TABLE'
       AND TABLE_CATALOG = 'mydb'

DECLARE @tblname VARCHAR(50)
SET @tblname = ''

OPEN db_cursor
FETCH NEXT FROM db_cursor INTO @tblname

WHILE @@FETCH_STATUS = 0
BEGIN
  IF CHARINDEX('mycommonwordforalltablesIwanttodothisto', @tblname) > 0
    BEGIN
      EXEC('DELETE FROM ' + @tblname)
      DBCC CHECKIDENT (@tblname, RESEED, 0)
    END

  FETCH NEXT FROM db_cursor INTO @tblname
END

CLOSE db_cursor
DEALLOCATE db_cursor
GO

Answer 19

Reseeding to 0 is not very practical unless you are cleaning up the table as a whole.

other wise the answer given by Anthony Raymond is perfect. Get the max of identity column first, then seed it with max.

Answer 20

It seems like the majority of replies here assumes that the table is empty and the Identity value needs to be reset. However, how I read the question is that @xorpower now has a table with records 1, 2, 3, 5, 6, 7, 12, 13, 14 etc...and wants a method to get that back to a contiguous list. (1, 2, 3, 4, 5, 6, 7, 8, 9 etc...)

cf But since I have to delete some records from the table, where some is the magic word here IMHO.

AFAIK there is no such a thing in MSSQL; worst case you can indeed dump the existing records table into a new table and go from there. The question to me to is also: why would you want to do that? And is an IDENTITY column then the best approach?

Anyway,the solutions provided here that do care about existing data are mostly about copying everything in a temp-table, TRUNCATE ing the existing table; reseeding the table and then copying everything back again. I'm sure that works but if you have a lot of data then this is a pretty heavy operation. Personally I would rather go with creating an identical table, copying the data in that new table (maybe in batches?) and then finally SWITCH ing the data to the original table and dropping the newly created table again. You're likely to need to do a CHECKIDENT after the SWITCH. This way you only need to move the data from one table to another once. To save space you could even DELETE the relevant records from the original table after a batch is copied.

PS: Yes, I know this is an old question, but given it's high points count it still shows up on top for similar questions and since nobody mentioned SWITCH yet it seemed worth adding.

Answer 21

DBCC CHECKIDENT ('[TestTable]', RESEED, 0); GO

Answer 22

Hello this stored procedure DELETE ALL ROWS of a table and check whether has identity column in the table,it will be reseed.

**** CAUTION: ALL ROWS WILL BE DELETED. *****

Create PROCEDURE ClearTableData 
    @TableName varchar(100)
AS
    EXEC ('ALTER TABLE '+@TableName+'  NOCHECK CONSTRAINT ALL ') 
    BEGIN TRY  
        EXEC ('Truncate Table'+@TableName )
        PRINT @TableName +' rows have trancated '
    END TRY  
    BEGIN CATCH  
        EXEC ('Delete From '+@TableName )
        PRINT @TableName +' rows have deleted '
    END CATCH  
    
    IF (OBJECTPROPERTY(OBJECT_ID(@TableName), 'TableHasIdentity'))  = 1 
            DBCC CHECKIDENT (@TableName, RESEED, 0) 

    EXEC ('ALTER TABLE '+@TableName+'  CHECK CONSTRAINT ALL ') 

GO

Answer 23

Use this sp for all tables:

reseed 'youtable'

after delete a record (in a trigger pe)

ALTER PROCEDURE [dbo].[RESEED](@Tabla nvarchar(100))

as

-- ********************* CREAR ESTA FUNCIÓN PRIMERO *******************************
/*
create function  dbo.FN_EsIdentidad(@Tabla nvarchar(100), @Campo nvarchar(100))
    returns int
    as
    begin
        return columnproperty ( object_id ( @Tabla  ), @Campo , 'IsIdentity')
    end 
GO
************************************************************************************
*/


declare @CampoIdentidad nvarchar(100)

    SELECT @CampoIdentidad  = Column_Name
        --,dbo.FN_EsIdentidad(Table_Name, Column_name) as EsIdentidad,
        --table_name, column_name 
        FROM information_schema.columns
        where dbo.FN_EsIdentidad(Table_Name, Column_name) = 1 
        and Table_Name=@Tabla


declare @Sql nvarchar(max)
declare @OutPutNum int
set @Sql = 'Select MAX(' + @CampoIdentidad + ') From ' + @Tabla
--select @CampoIdentidad


set @sql = 'Select @ValorOut=max(' + @CampoIdentidad + ') From ' + @Tabla 
declare @ParamDefinition nvarchar(max)
SET @ParamDefinition = '@ValorOut int OUTPUT'

EXECUTE sp_executesql  
    @SQL 
    ,@ParamDefinition  
    ,@ValorOut = @OutPutNum OUTPUT;  

--select @OutPutNum
set @OutPutNum  = coalesce(@OutPutNum ,0)
DBCC CHECKIDENT (@Tabla, RESEED, @OutputNum)

Answer 24

you can CHECKIDENT To Reset Seed

DBCC CHECKIDENT ( table_name [, { NORESEED | { RESEED [, new_reseed_value ] } } ] ) [ WITH NO_INFOMSGS ]

Example

DBCC CHECKIDENT ('TAble', reseed,0)

-- Example Query

--Create Table DROP TABLE IF EXISTS ExampleTable create table ExampleTable (Id Bigint identity(1,1), Name nvarchar(10))

--Insert to ExampleTable and Delete and Show identity insert into ExampleTable (Name) select 'Test1' as NAme union all select 'Test2' as NAme

select * from ExampleTable

delete from ExampleTable

insert into ExampleTable (Name) select 'Test3' as NAme

select * from ExampleTable

delete from ExampleTable

--Find seedTable declare @reseed int=0

--Reset seed Table to Zero when table is empty

if(not exists( select top 1 * from ExampleTable)) begin

 SELECT 
    @reseed=cast( seed_value as int)
FROM sys.tables tables 
    JOIN sys.identity_columns identity_columns 
ON tables.object_id=identity_columns.object_id
where 
    tables.name='ExampleTable' 
and OBJECT_SCHEMA_NAME(tables.object_id, db_id())='dbo'

  set @reseed=@reseed -1

end else begin --if Table Has Data and use Max id For seed set @reseed=(select top 1 id from ExampleTable order by id desc)

end

DBCC CHECKIDENT ('ExampleTable', reseed,@reseed)

insert into ExampleTable (Name) select 'Test4' as NAme

select * from ExampleTable

GO

Answer 25

Its always better to use TRUNCATE when possible instead of deleting all records as it doesn't use log space also.

In case we need delete and need to reset the seed, always remember that if table was never populated and you used DBCC CHECKIDENT('tablenem',RESEED,0) then first record will get identity = 0 as stated on msdn documentation

In your case only rebuild the index and don't worry about losing the series of identity as this is a common scenario.

Answer 26

First : Identity Specification Just : "No" >> Save Database Execute Project

After then : Identity Specification Just : "YES" >> Save Database Execute Project

Your Database ID, PK Start from 1 >>