Index Autoincrement for Microsoft SQL Server 2008 R2

Index autoincrement for Microsoft SQL Server 2008 R2

In SQL Server, it's not a separate datatype ("autoincrement") - but you can define an INT column to be an IDENTITY.

How are you creating your table - visual designer or T-SQL script??

In T-SQL, you would use:

CREATE TABLE dbo.MyTable(ID INT IDENTITY(1,1) ......

and in the visual table designer, you need to check:

It's an option for a column of type INT - you can define the seed (starting value) and the increment - typically both are set to 1.

Reset autoincrement in Microsoft SQL Server 2008 R2

If you use the DBCC CHECKIDENT command:

 DBCC CHECKIDENT ("YourTableNameHere", RESEED, 1);

But use with CAUTION! - this will just reset the IDENTITY to 1 - so your next inserts will get values 1, then 2, and then 3 --> and you'll have a clash with your pre-existing value of 3 here!

IDENTITY just dishes out numbers in consecutive order - it does NOT in any way make sure there are no conflicts! If you already have values - do not reseed back to a lower value!

Auto-increment primary key in SQL tables

1. Presumably you are in the design of the table. If not: right click the table name - "Design".
2. Click the required column.
3. In "Column properties" (at the bottom), scroll to the "Identity Specification" section, expand it, then toggle "(Is Identity)" to "Yes".

Auto increment primary key in SQL Server Management Studio 2012

Make sure that the Key column's datatype is int and then setting identity manually, as image shows

Or just run this code

-- ID is the name of the  [to be] identity column
ALTER TABLE [yourTable] DROP COLUMN ID 
ALTER TABLE [yourTable] ADD ID INT IDENTITY(1,1)

the code will run, if ID is not the only column in the table

image reference fifo's

Autoincrement uniqueidentifier

Or even better: use the newsequentialid() as the default for your UNIQUEIDENITIFER column. That'll give you a somewhat sequential series of GUIDs.

CREATE TABLE dbo.YourTable   
   (SerialID UNIQUEIDENTIFIER 
        CONSTRAINT DF_SerialID DEFAULT newsequentialid(),
     .... (other columns)......
   )

Trouble is: newsequentialid is only available as a column default - you cannot call it as a function or anything. But that seems to fit your requirements.

UPDATE: there appears to be an acknowledged bug in SQL Server Management Studio that prevents specifying newsequentialid() as the default for a column in the interactive table designer.

See: http://social.msdn.microsoft.com/Forums/en-US/sqltools/thread/cad8a4d7-714f-44a2-adb0-569655ac66e6

Workaround: create your table without specifying any default, and then type in this T-SQL statement in a normal query window and run it:

ALTER TABLE dbo.YourTable
    ADD CONSTRAINT DF_SerialID DEFAULT newsequentialid() FOR SerialID

That should do the trick!

BULK INSERT with identity (auto-increment) column

Don't BULK INSERT into your real tables directly.

I would always

1. insert into a staging table dbo.Employee_Staging (without the IDENTITY column) from the CSV file
2. possibly edit / clean up / manipulate your imported data

3. and then copy the data across to the real table with a T-SQL statement like:

   INSERT INTO dbo.Employee(Name, Address) 
      SELECT Name, Address
      FROM dbo.Employee_Staging
   

For autoincrement fields: MAX(ID) vs TOP 1 ID ORDER BY ID DESC

In theory, they will use same plans and run almost same time.

In practice,

SELECT TOP 1 Id FROM Table1 ORDER BY Id DESC

will more probably use a PRIMARY KEY INDEX.

Also, this one is more extendable if you will decide to select some else column along with id.

An actual plan on MAX() says:

SELECT <- AGGREGATE <- TOP <- CLUSTERED INDEX SCAN

, while plan for TOP 1 says:

SELECT <- TOP <- CLUSTERED INDEX SCAN

, i. e. aggregate is omitted.

Aggregate actually won't do anything here, as there is but one row.

P. S. As @Mehrdad Afshari and @John Sansom noted, on a non-indexed field MAX is slightly faster (of course not 20 times as optimizer says):

-- 18,874,368 rows

SET LANGUAGE ENGLISH
SET STATISTICS TIME ON
SET STATISTICS IO ON
PRINT 'MAX'
SELECT MAX(id) FROM master
PRINT 'TOP 1'
SELECT TOP 1 id FROM master ORDER BY id DESC
PRINT 'MAX'
SELECT MAX(id) FROM master
PRINT 'TOP 1'
SELECT TOP 1 id FROM master ORDER BY id DESC
PRINT 'MAX'
SELECT MAX(id) FROM master
PRINT 'TOP 1'
SELECT TOP 1 id FROM master ORDER BY id DESC
PRINT 'MAX'
SELECT MAX(id) FROM master
PRINT 'TOP 1'
SELECT TOP 1 id FROM master ORDER BY id DESC
PRINT 'MAX'
SELECT MAX(id) FROM master
PRINT 'TOP 1'
SELECT TOP 1 id FROM master ORDER BY id DESC

Changed language setting to us_english.

SQL Server Execution Times:
   CPU time = 0 ms,  elapsed time = 1 ms.

SQL Server Execution Times:
   CPU time = 0 ms,  elapsed time = 1 ms.

SQL Server Execution Times:
   CPU time = 0 ms,  elapsed time = 1 ms.
MAX

SQL Server Execution Times:
   CPU time = 0 ms,  elapsed time = 20 ms.

(строк обработано: 1)
Table 'master'. Scan count 3, logical reads 32655, physical reads 0, read-ahead reads 447, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.

SQL Server Execution Times:
   CPU time = 5452 ms,  elapsed time = 2766 ms.
TOP 1

SQL Server Execution Times:
   CPU time = 0 ms,  elapsed time = 1 ms.

(строк обработано: 1)
Table 'master'. Scan count 3, logical reads 32655, physical reads 0, read-ahead reads 2, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.

SQL Server Execution Times:
   CPU time = 6813 ms,  elapsed time = 3449 ms.
MAX

SQL Server Execution Times:
   CPU time = 0 ms,  elapsed time = 1 ms.

(строк обработано: 1)
Table 'master'. Scan count 3, logical reads 32655, physical reads 0, read-ahead reads 44, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.

SQL Server Execution Times:
   CPU time = 5359 ms,  elapsed time = 2714 ms.
TOP 1

SQL Server Execution Times:
   CPU time = 0 ms,  elapsed time = 1 ms.

(строк обработано: 1)
Table 'master'. Scan count 3, logical reads 32655, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.

SQL Server Execution Times:
   CPU time = 6766 ms,  elapsed time = 3379 ms.
MAX

SQL Server Execution Times:
   CPU time = 0 ms,  elapsed time = 1 ms.

(строк обработано: 1)
Table 'master'. Scan count 3, logical reads 32655, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.

SQL Server Execution Times:
   CPU time = 5406 ms,  elapsed time = 2726 ms.
TOP 1

SQL Server Execution Times:
   CPU time = 0 ms,  elapsed time = 1 ms.

(строк обработано: 1)
Table 'master'. Scan count 3, logical reads 32655, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.

SQL Server Execution Times:
   CPU time = 6780 ms,  elapsed time = 3415 ms.
MAX

SQL Server Execution Times:
   CPU time = 0 ms,  elapsed time = 1 ms.

(строк обработано: 1)
Table 'master'. Scan count 3, logical reads 32655, physical reads 0, read-ahead reads 85, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.

SQL Server Execution Times:
   CPU time = 5392 ms,  elapsed time = 2709 ms.
TOP 1

SQL Server Execution Times:
   CPU time = 0 ms,  elapsed time = 1 ms.

(строк обработано: 1)
Table 'master'. Scan count 3, logical reads 32655, physical reads 0, read-ahead reads 10, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.

SQL Server Execution Times:
   CPU time = 6766 ms,  elapsed time = 3387 ms.
MAX

SQL Server Execution Times:
   CPU time = 0 ms,  elapsed time = 1 ms.

(строк обработано: 1)
Table 'master'. Scan count 3, logical reads 32655, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.

SQL Server Execution Times:
   CPU time = 5374 ms,  elapsed time = 2708 ms.
TOP 1

SQL Server Execution Times:
   CPU time = 0 ms,  elapsed time = 1 ms.

(строк обработано: 1)
Table 'master'. Scan count 3, logical reads 32655, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.

SQL Server Execution Times:
   CPU time = 6797 ms,  elapsed time = 3494 ms.

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