How do you drop a default value from a column in a table?

Question

How do you alter a column to remove the default value?

The column was created with:

 ALTER table sometable Add somecolumn nchar(1) NOT NULL DEFAULT 'N' 

And then altered with:

 alter table sometable alter column somecolumn nchar(1) null 

That allows nulls, but the default value remains. How can you remove it?

Answer 1

Its a default constraint, you need to perform a:

ALTER TABLE {TableName}  DROP CONSTRAINT ConstraintName 

If you didn't specify a name when you created the constraint, then SQL Server created one for you. You can use SQL Server Management Studio to find the constraint name by browsing to the table, opening its tree node, then opening the Constraints node.

If I remember correctly, the constraint will be named something along the lines of DF_SomeStuff_ColumnName.

EDIT: Josh W.'s answer contains a link to a SO question that shows you how to find the auto generated constraint name using SQL instead of using the Management Studio interface.

Answer 2

This is what I came up with (before seeing Josh W. answer, well actually I saw it but skimmed it so fast I misunderstood it):

declare @name nvarchar(100) select @name = [name] from sys.objects where type = 'D' and parent_object_id = object_id('sometable')  if (@name is not null)   begin      exec ('alter table [sometable] drop constraint [' + @name +']')   end 

The advantage I have here is that I know that there is only one such constraint on the whole table. If there had been two, well I guess that is why you are supposed to name them ;).

(The issues is that that this is a modification made to 10 different customer databases, so there isn't one consistent name to put in a script)