Delete/drop columns with foreign key constraints or default values constraints in SQL server.

drop_columns_with_constraints.sql

-- Search default value constraints:
SELECT 
  obj.name 
FROM 
  sys.objects AS obj 
JOIN 
  sys.columns AS clm ON obj.object_id = clm.default_object_id 
WHERE 
  obj.type = 'D' AND obj.parent_object_id = OBJECT_ID('User') AND clm.name = 'CompanyId';
  
-- Search foreign key constraints:
SELECT
	fs.name AS 'Foreign Key',
	s.name + '.' + t.name AS 'Table Name'
FROM
	sys.foreign_keys fs
INNER JOIN sys.tables t
	ON t.object_id = fs.parent_object_id
INNER JOIN sys.schemas s
	ON s.schema_id = t.schema_id;

-- Drop constraints and Drop column:
ALTER TABLE User DROP CONSTRAINT DF__User__HasCr__12B12345;
ALTER TABLE User DROP COLUMN CompanyId;