Question

I am student of RDBMS.

I have very basic question let say I have one existing Table in SQL server. What will be script to alter table.

• Drop Column ‘RowId’ if exist.
• Drop contraint if exist.
• Add one new column ‘RowId’ into table.
• Make this column as primary key.
• Autoincrement type int.

Answer 1

In SQL Server 2005 or newer, you could use this script:

-- drop PK constraint if it exists
IF EXISTS (SELECT * FROM sys.key_constraints WHERE type = 'PK' AND parent_object_id = OBJECT_ID('dbo.YourTable') AND Name = 'PK_YourTable')
   ALTER TABLE dbo.YourTable
   DROP CONSTRAINT PK_YourTable
GO

-- drop column if it already exists
IF EXISTS (SELECT * FROM sys.columns WHERE Name = 'RowId' AND object_id = OBJECT_ID('dbo.YourTable'))
    ALTER TABLE dbo.YourTable DROP COLUMN RowId
GO

-- add new "RowId" column, make it IDENTITY (= auto-incrementing)
ALTER TABLE dbo.YourTable 
ADD RowId INT IDENTITY(1,1)
GO

-- add new primary key constraint on new column   
ALTER TABLE dbo.YourTable 
ADD CONSTRAINT PK_YourTable
PRIMARY KEY CLUSTERED (RowId)
GO

Of course, this script may still fail, if other tables are referencing this dbo.YourTable using foreign key constraints onto the pre-existing RowId column…

Update: and of course, anywhere I use dbo.YourTable or PK_YourTable, you have to replace those placeholder with the actual table / constraint names from your own database (you didn’t mention what they were, in your question…..)