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Understanding Auto Increment in SQL Server

In this article we will talk about the auto increment primary key in SQL Server Databases.

Auto increment Primary Key is used in SQL Server - to allow a unique and not null no to be generated when a new record is inserted in table for a particular tuple.

There's no such thing as AUTONUMBER in SQL Server, What there is, is the IDENTITY property, which allows for the automatic creation of new records, such as for PKs, and IDENTITY is just a generator.

It starts at a First value and counts upwards. When the existing records are deleted in the table which has auto increment number the next available number shows ‘0’ on the form, if a record insert directly to the table from then onwards it identifies the auto increment number correctly on the form.

Example: Suppose that we had 100 records in the SQL SERVER table before delete and although the next number would be 6 but in Employee, it shows as ‘0’.

IDENTITY:

It identifies that the new tuple is an identity tuple.When a new row is added to the table, the Database Engine provides a unique, and not null incremental value for the column. This tuples are typically used with PK constraints to serve as the unique row identifier for the SCOPE_IDENTITY like:

SCOPE_IDENTITY gives the last IDENTITY value inserted into an IDENTITY column in the same scope table. The IDENTITY property can be inserted to datatypes like smallint, bigint, int, decimal (15, 0), or numeric (15, 0) columns. Only 1 identity column can be created per table.Co-related defaults and DEFAULT constraints can’t be used with an identity tuple. All of them tuples and incremented measuring or never can be identified. When Never is specified the default is (1, 1).

THE CODING SNIPPETS OF IDENTITY ARE FOLLOWING:

Listing 1: Code Snippets

CREATE TABLE EmpMst
(
ID int IDENTITY(1,1) PRIMARY KEY,
LstNme varchar(100) NOT NULL,
FrstNme varchar(100),
Addi varchar(100),
CityLoc varchar(100)
)

Statement to Create Table:

CREATE TABLE InvoiceTrn(
   InvoceNo INT IDENTITY(1,1) PRIMARY KEY
  Prodct VARCHAR(55))

Insert Statement:

INSERT INTO Buy
   (Prodct)
  VALUES
   ('Test Prodct A')
GO

Get the auto-generated InvoiceNo for last inserted record

SELECT @@IDENTITY as [InvoiceTrnNo]

Developers who are used to AutoNumber columns in MS Access or Identity columns in SQL Server often complain when they have to manually populate primary key columns using steps under Oracle.

The trigger can be edited to give slightly different ouputs. If the insert trigger needs to perform more functionality than this one job you may wish to do something like the following:

Listing 2: Trigger Example

CREATE OR REPLACE TRIGGER domain_epl 
BEFORE INSERT ON domn 
FOR EACH ROW
BEGIN
  SELECT NVL(:new.id, dept_seq.NEXTVAL)
  INTO   :new.id
  FROM   dual;
  -- Do more processing here.
END;

THE BENEFITS ARE:

We can use the value of the PK field to be created automatically every time a new record is included. Auto - Increment this unique word is used for auto increment feature. Normally, the starting value for Auto- Increment is one, and it will increment by one for each record.

The coding snippets are following:

Listing 3: Coding Snippets

CREATE TABLE IDnDB
( pk_ID Integer IDENTITY(1,1)
, Textdata Varchar(100) )

SET IDENTITY_INSERT IDnDB OFF
SET IDENTITY_INSERT IDnDB ON
INSERT IDnDB (pk_ID, Textdata) Values (3, 'This works')
SET IDENTITY_INSERT IDnDB OFF
EXEC ('SET IDENTITY_INSERT IDnDB ON')
INSERT IDnDB (pk_ID, Textdata) Values (4, 'This fails')
Select *
From IDnDB
Drop Table IDnDB
In Oracle:
create sequence prac_se 
start with 1 
increment by 1 
nomaxvalue
Followed by
insert into test values(prac_se.nextval, 'Hello!');
OR
create trigger testtrig
before insert on test
for each row
begin
select prac_se.nextval into :new.id from dual;
end;

IN MSACCESS:

A unique and not null sequential (increment by One) number or random number generated by MSAccess whenever a new record is added to a tuple. AutoNumber fields can't be inserted or updated for information -4 bytes (16 bytes if the tuple property is set to ReplID).

Your starting number must be less than 1,000,000, i.e. that the most that you can insert it out at is 999,999,999. i.e. that in the bad configure, you could make you would still be able to create 9 billion records (9,999,999,999 - 999,999,999) before you'd reach the highest allowed.

We just use all of our tables to a SQL Server database and are looking to continue using MS Access as a frontend tool because of the UI. We do, however, have a couple of tuples that use the AutoNumber type which I have learned SQL Server simply converted to the "bigint" data type.

Now, I've already marked out how to make views that utilize the "CAST" function to convert away from "bigint" when I am linking my tables from the database(this is so that MS ACCESS can generate the tuples rather than giving me #deleted values), however this leaves my tuples of course with no AutoNumber option still. Is there any solution for this! I am really like to continue using an auto incremental column to be used as a PK for our jobs with these tuples.

Listing 4: Using PK

CREATE TABLE IDDemo
( pk_ID Integer IDENTITY(1,1)
, Textdata Varchar(100) )
SET IDENTITY_INSERT IDDemo OFF
SET IDENTITY_INSERT IDDemo ON
INSERT IDDemo (pk_ID, Textdata) Values (3, 'This works')
SET IDENTITY_INSERT IDDemo OFF
EXEC ('SET IDENTITY_INSERT IDDemo ON')
INSERT IDDemo (pk_ID, Textdata) Values (4, 'This fails')
Select *
From IDDemo
Drop Table IDDemo
1)
SET IDENTITY_INSERT NewDB.Extensions.FieldSelectionGroups ON
GO
INSERT INTO NewDB.Extensions.FieldSelectionGroups 
SELECT *
FROM OLDDB.Extensions.FieldSelectionGroups with (HOLDLOCK TABLOCKX)
GO
SET IDENTITY_INSERT NewDB.Extensions.FieldSelectionGroups OFF 
GO


2)
SET IDENTITY_INSERT NewDB.Extensions.FieldSelectionGroups ON
GO
INSERT INTO NewDB.Extensions.FieldSelectionGroups 
SELECT *
FROM OLDDB.Extensions.FieldSelectionGroups
GO
SET IDENTITY_INSERT NewDB.Extensions.FieldSelectionGroups OFF 
GO

The select list for the INSERT statement contains fewer items than they include item.

Listing 5: The no of SELECT entry have to same with the no of INSERT columns.

Create Table #temp
(RowID int identity(1,1) not null,
MyID int not null,
MyName varchar(50) not null
)

Insert into #temp (RowID, MyID, MyName)
Select 1, 'Name'

select *
from #temp

drop table #temp1
[FutureArticleId] [bigint] IDENTITY(1,1) NOT NULL,
[cFutureArticleTitle] [nvarchar](50) COLLATE SQL_Latin1_General_CP1_CI_AS NOT NULL,
[cDes] [ntext] COLLATE SQL_Latin1_General_CP1_CI_AS NOT NULL, [gId] [bigint] NOT NULL,
[cKeywd] [ntext] COLLATE SQL_Latin1_General_CP1_CI_AS NULL, [bIsDelet] [bit] NOT NULL CONSTRAINT [DF_tbl_nexttopic_bIsDeleted] DEFAULT ((0)), [tOnprepare] [datetime] NOT NULL,
[tOnmodify] [datetime] NULL, [gmadeby] [bigint] NOT NULL, [gmodifiedby] [bigint] NULL,

After some entry and delete from the frontend, definitely there are holes in the next topic column which is an identitycolumn.

When entering the records in unique and null column that means PK column, the values are being entered into the null position and not in the next available PK values.

This means you can start at one (1) and increment by one (1) or you can pick something else like -9,223,372,036,854,775,808 (the smallest possible bigint number) and then increment by 1 up to the same number in the positive range and be able to add trillions or rows.

As to whether or not it's a primary key, that's a different topic. We have an identity column and not mark it as the PK or a clustered index. We should remember that we have one identity column per table.

In SQL Server 2012, which has released, we can create a sequence, similar to Oracle. This can be accessed by many tables or even just code to get an increasing value.We has more than one sequence in a table.

Listing 6: Creating Sequence

IF EXISTS (SELECT * FROM sys.objects WHERE object_id = OBJECT_ID(N'[dbo].[uspResetIdentities]') AND type in (N'P', N'PC'))
DROP PROCEDURE [dbo].[uspResetIdentities]
go
SET ANSI_NULLS ON
SET QUOTED_IDENTIFIER ON
GO
Reset of Identity:
CREATE PROCEDURE Reset
/* 
begin trans
exec Reset
rollback transaction
*/
as
set nocount on 
declare curl cursor readonly for 
SELECT OB.name AS [Table], COL.name AS [Field]
FROM sysobjects OB 
INNER JOIN syscolumns COL ON OB.id = COL.id
WHERE (COLUMNPROPERTY(OB.id, COL.name, 'IsIdentity') = 1) 
AND (OB.name <> 'dtproperties')
and OB.xtype='U'
declare @strS nvarchar(500), @strParams nvarchar(255)
declare @strTblNm nvarchar(100), @strFieldNm nvarchar(100)
declare @intMa int; set @intMa=-1
open curI
while (1=1) 
begin
fetch next from curI into @strTblNm, @strFieldNm
if @@fetch_status<>0 break
set @strS='select @pintMa = 1 + isnull(max(' + @strFieldNm + '),0) from ' + @strTblNm 
set @strPram = N'@pintMa bigint output'
exec sp_executeSQL @strS, @strPram, @pintMa = @intMa output
print ''
DBCC CHECKIDENT (@strTblNm, RESEED, @intMa)
print '** Reset identity for ' + @strTblNm + ' to ' + Cast(@intMa as varchar) + ' **'
end
close curI; deallocate curI
set nocount off.

Conclusion:

So far we have discussed the different aspects of Auto increment number in Numeric Tuple or Auto Identity in SQL Server. From above said discussions we made an opinion that in respect of small database Auto Increment column is good but for big database or previous record counting database is not so fit in Auto increment column or Identity Column.



Website: www.techalpine.com Have 16 years of experience as a technical architect and software consultant in enterprise application and product development. Have interest in new technology and innovation area along with technical...

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