SQL server query to drop default constraint and a column

declare @default sysname, @sql nvarchar(max)

select @default = name
from sys.default_constraints
where parent_object_id = object_id('MYTABLENAME')
AND type = 'D'
AND parent_column_id = (
select column_id
from sys.columns
where object_id = object_id('MYTABLENAME')
and name = 'MYCOLUMNNAME'
)

set @sql = N'alter table MYTABLENAME drop constraint ' + @default
exec sp_executesql @sql

alter table MYTABLENAME drop MYCOLUMNNAME

go