Question

I’m building a SQL script to reset a database. To do this I want to empty several (not all) tables and reset their identity values to 0.

For some tables I use TRUNCATE TABLE, but this does not work when the table has is referenced by a foreign key constraint. For those tables I use DBCC CHECKIDENT(TableName, RESEED, 0). This works for most tables, but not for all. If a table never had any data, the current identity value is NULL instead of 0:

CREATE TABLE TableName (Id int identity, Value varchar(10))
DBCC CHECKIDENT(TableName)

-- Checking identity information: current identity value 'NULL', current column value 'NULL'.

If I use DBCC CHECKIDENT(TableName, RESEED, 0) on them, they will have 0 as next identity value. I can instead use 1 as reseed value, but then the tables which have had data in them will start on 2.

Is it possible to find the next identity value in any of the sys-views? If I just could get next value into a variable, I could use it to set next value to either 0 or 1. I’ve tried with IDENT_CURRENT('TableName') but it says 1 for both NULL and 0 as next value.

And please, I don’t want any questions like “why do you need all of them to start from 1” or any other question suggesting another result than the one I’m asking for.

Answer 1

Use if all tables have identity field.

exec sp_MSforeachtable @command1 = 'DBCC CHECKIDENT(''?'', RESEED, 1)'

MSforeachtable is an undocumented, but extremely handy stored proc which executes a given command against all tables in your database.

To reseed ONLY tables with an identity column you can use the next script.
It also makes use of sp_MSforeachtable but taking into account the correct tables.

EXEC sp_MSforeachtable '
IF (SELECT COUNT(1) 
    FROM INFORMATION_SCHEMA.TABLES 
    WHERE TABLE_TYPE = ''BASE TABLE'' 
    AND ''[''+ TABLE_SCHEMA + ''].['' + TABLE_NAME + '']'' = ''?'' 
    AND OBJECTPROPERTY(OBJECT_ID(TABLE_NAME), ''TableHasIdentity'') = 1) > 0 
BEGIN
    DBCC CHECKIDENT (''?'', RESEED, 1)
END'

Use Following query to get Last Identity value inserted in tables in a database.

   SELECT TableName = OBJECT_NAME(OBJECT_ID) ,
       ColumnName = name ,
       OriginalSeed = seed_value ,
       Step = increment_value ,
       LastValue = last_value ,
       IsNotForReplication = is_not_for_replication
FROM sys.identity_columns

Refer this for more details