tsql - SQL Server default values: why with one or two parentheses?

Question

if you run this script to retrieve all default value definations in a database:

select 
    c.name as columnname, t.name as tablename, 
    d.definition as value, d.name as constraintname
from
    sys.default_constraints d
    join sys.columns c
        on d.parent_column_id = c.column_id
        and d.parent_object_id = c.object_id
    join sys.tables t
        on c.object_id = t.object_id

you would get a lot default values like:

(getdate())
((0))
('')
('2099-12-31')

My question is, why are there parentheses? Are they nessessary? Why some values have one pair of them, others have two? Is the count to be followed exactly when scripting T-SQL?

Answer 1

It's just how SQL stores them internally.

They aren't needed except for when IN is expanded to (.. OR ...) for some reason.

You should try a check constraint with ANDs and ORs. Lordy lord.