How to alter column from int to Uniqueidentifier in SQL Server 2008
<p>I have a table with column "ID" as datatype int. </p>

<pre><code>CREATE TABLE [dbo].[STUDENT]
(
    [ID] [int] IDENTITY(1,1) NOT NULL,
    [DOB] [datetime] NOT NULL ,
    [NAME] [nvarchar](250) NULL,
    [CLASS] [nvarchar](50) NULL,

    CONSTRAINT [PK_STUDENT_DATA] 
         PRIMARY KEY CLUSTERED ([ID] ASC)
                     WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, 
                           IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, 
                           ALLOW_PAGE_LOCKS = ON, FILLFACTOR = 95) ON [PRIMARY]
)  ON [PRIMARY]
</code></pre>

<p>Now I want to change datatype from <code>int</code> to <code>uniqueidentifier</code>. I have deleted constraint <code>PK_STUDENT_DATA</code>. My <code>ALTER</code> statement is </p>

<pre><code>ALTER TABLE dbo.STUDENT COLUMN ID uniqueidentifier
</code></pre>

<p>I am getting error:</p>

<blockquote>
  <p>Identity column 'HISTORY_ID' must be of data type int, bigint,
  smallint, tinyint, or decimal or numeric with a scale of 0, and
  constrained to be nonnullable.</p>
</blockquote>