if not exists (
select *
from sys.all_columns c
join sys.tables t on t.object_id = c.object_id
join sys.schemas s on s.schema_id = t.schema_id
join sys.default_constraints d on c.default_object_id = d.object_id
where t.name="table"
and c.name="column"
and s.name="schema")
....