Skip to main content

Identity Column - SQL Server

 Identity column in SQL server

IDENTITY property used to create an identity column in a table. It will be used with the CREATE TABLE and ALTER TABLE Transact-SQL statements. This column should be integer based column which will be handled by SQL server.

Syntax

            IDENTITY [ (seed , increment) ]

seed
Is the value that is used for the very first row loaded into the table.

increment
Is the incremental value that is added to the identity value of the previous row that was loaded.

You must specify both the seed and increment or neither. If neither is specified, the default is (1,1).

Example

            CREATE TABLE Student

( 

 RollNumber int IDENTITY(1,1), 

 name varchar (50), 

 ..); 

You must specify both the seed and increment or neither. If neither is specified, the default is (1,1).

Remarks

Identity columns can be used for generating key values. The identity property on a column guarantees the following:

·       Each new value is generated based on the current seed & increment.

·       Each new value for a particular transaction is different from other concurrent transactions on the table.

The identity property on a column does not guarantee the following:

·       Uniqueness of the value - Uniqueness must be enforced by using a PRIMARY KEY or UNIQUE constraint or UNIQUE index.

 ·       Consecutive values within a transaction - A transaction inserting multiple rows is not guaranteed to get consecutive values for the rows because other concurrent inserts might occur on the table. If values must be consecutive then the transaction should use an exclusive lock on the table or use the SERIALIZABLE isolation level.

·       Consecutive values after server restart or other failures - SQL Server might cache identity values for performance reasons and some of the assigned values can be lost during a database failure or server restart. This can result in gaps in the identity value upon insert. If gaps are not acceptable then the application should use its own mechanism to generate key values. Using a sequence generator with the NOCACHE option can limit the gaps to transactions that are never committed.

·       Reuse of values - For a given identity property with specific seed/increment, the identity values are not reused by the engine. If a particular insert statement fails or if the insert statement is rolled back then the consumed identity values are lost and will not be generated again. This can result in gaps when the subsequent identity values are generated.

Reference :

              https://learn.microsoft.com/en-us/sql/t-sql/statements/create-table-transact-sql-identity-property?view=sql-server-ver16

             

Labels:

Comments

Post a Comment

Popular posts from this blog

Data type precedence - SQL Server

       In SQL Server, data type precedence determines which data type takes precedence over others when two or more data types are combined or compared. It is important to understand data type precedence to ensure that the correct data type is used and that data is not lost or truncated during operations. In this blog, we will discuss data type precedence in SQL Server with examples. Data type precedence levels SQL Server has 16 data type precedence levels, with the highest level being 1 and the lowest level being 16. The data type with the lowest precedence is considered to be the "weakest" data type and is most likely to be converted to a higher precedence data type during operations. Here is the list of data types in SQL Server, ordered by their precedence levels: user-defined data types (highest precedence) sql_variant xml datetimeoffset datetime2 datetime smalldatetime date time float real decimal/numeric money/smallmoney bigint/i...
Post a Comment
Read more

SFTP Integration in SSIS package Using WinSCP DLL

  In this blog, I am planning to write about SSIS SFTP Task details and reference sites, upload and download the files from SFTP server using SSIS package with help of the winscp library. Steps to configure the winscp DLL and Download Files 1.        Please download the DLL and required files from below path https://winscp.net/eng/downloads.php#additional 2.        Once Downloaded, use the below comments to add in Local GAC "Path to the gacutil exe \gacutil.exe" /i WinSCPnet.dll 3.        Please use the below URL as guide to implement the SSIS script task to download the files from SFTP using winscp as library https://winscp.net/eng/docs/library_ssis 4.        I am just briefing the steps based on the above URL what we can try in SSIS package. 5.        Please create the below variables in SSIS package which we need ...
Post a Comment
Read more

XML data type Functions – SQL Server

 The XML data type in MSSQL Server is a powerful tool for handling and manipulating XML data within a relational database system. In addition to storing XML data as a column in a table, SQL Server provides a number of XML functions and methods that allow for easy parsing, querying, and transformation of XML data. In this blog post, we will cover all XML data type methods available in MSSQL Server. value() Method: The value() method is used to extract a single value from an XML instance. This method accepts an XQuery expression as a parameter, which is used to identify the value to be extracted. The syntax of the value() method is as follows: xml . value ( XQuery expression , Data type ) For example, the following query extracts the value of the 'name' element from an XML column called 'MyXMLColumn': SELECT MyXMLColumn . value ( '(/Root/Person/Name)[1]' , 'varchar(50)' ) AS Name FROM MyTable   query() Method: The query() method i...
Post a Comment
Read more