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

User · Answer

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

User · Answer

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   gt  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

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Reset identity column with new id     DECLARE  MAX INT SELECT  MAX ISNULL MAX Id  0  FROM  TestTable   DBCC CHECKIDENT    TestTable    RESEED  MAX

User · Answer

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

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DBCC CHECKIDENT   lt TableName gt   reseed  0    This will set the current identity value to 0   On inserting the next value  the identity value get incremented to 1

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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  i e  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     gt  1         DBCC CHECKIDENT   dbo Tbl   RESEED  0      ELSE         DBCC CHECKIDENT   dbo Tbl   RESEED  1        ELSE     DBCC CHECKIDENT   dbo Tbl   RESEED   maxID

User · Answer

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

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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

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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  amp  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

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It should be noted that IF all of the data is being removed from the table via the DELETE  i e  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

User · Answer

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

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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

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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

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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

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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

User · Answer

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

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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

User · Answer

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

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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

User · Answer

DBCC CHECKIDENT   TestTable   RESEED  0  GO   Where 0 is identity Start value

[sql] Reset identity seed after deleting records in SQL Server

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