If you have created a table in Microsoft SQL and along with a table you have a column with a default value, then the name of the constraint will be generate by the SQL framework unless given. This will be will have some random GUID which will keep it hard to know when you want to drop a column. There could be certain sitations where you want to directly delete the column and there are situations where the column should be dropped without having the knowldge of constaint name.
You can acheive that by using the following sql
DECLARE @ConstraintName nvarchar(200)
BEGIN
SELECT @ConstraintName = Name
FROM SYS.DEFAULT_CONSTRAINTS
WHERE PARENT_OBJECT_ID = OBJECT_ID('TABLE____NAME')
AND PARENT_COLUMN_ID =
(SELECT column_id
FROM sys.columns
WHERE NAME = N'COLUMN_____NAME'
AND object_id = OBJECT_ID(N'TABLE____NAME')
) if(@ConstraintName IS NOT NULL)
BEGIN EXEC(
'ALTER TABLE TABLE____NAME DROP CONSTRAINT ' + @ConstraintName
)
ALTER TABLE TABLE____NAME
DROP COLUMN COLUMN_____NAME
END