Retrieve and delete a default constrain from a column

Using the following SP, you can dynamically find default constraint of a column and drop that.

CREATE PROC dbo.DropDefaultConstraints
(
  @schema_name NVARCHAR(250),
  @table_name NVARCHAR(256),
  @col_name NVARCHAR(256)
)
AS
BEGIN

  DECLARE @Command  NVARCHAR(1000)
  SELECT @Command = 'ALTER TABLE ' + @schema_name +'.'+ @table_name + ' DROP CONSTRAINT ' + d.name
  FROM sys.tables t  
  JOIN    sys.default_constraints d      
   ON d.parent_object_id = t.object_id 
  JOIN    sys.columns c     
   ON c.object_id = t.object_id     
    AND c.column_id = d.parent_column_id
   WHERE t.name = @table_name AND c.name = @col_name
   PRINT @Command
   EXECUTE (@Command)

END
GO

Result :  ALTER TABLE dbo.Person DROP CONSTRAINT DF_Person_Nationality
ref: stackoverflow.com