Thursday, June 17, 2010

What is $IDENTITY?

This was in one of my slides of SQL Brain Bashers presentation which was done at SQL Server User Group Meeting.

What is $IDENTITY? Everybody knows that we use IDENTITY property on columns where we need automatically incrementing identification number. The $IDENTITY does not set anything, but allows us to reference the column using it. Here is an example;

CREATE TABLE dbo.Employee
    EmployeeKey int IDENTITY(1,1) PRIMARY KEY
    ,FirstName varchar(50) NULL
    ,LastName varchar(50) NOT NULL

When query for column like EmployeeKey, $IDENTITY can be used instead on column name;

-- both queries return same resultset
SELECT EmployeeKey, LastName
FROM dbo.Employee
FROM dbo.Employee

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