How to select default value that was created as create default and then was binded to user defined data type? - sql

Question

There is a table with all fields of user defined data types and NOT NULL. There are some defaults created as CREATE DEFAULT and binded to those user defined data types. It is given that way and I may not change it.
I need to insert data into this table from the source where there are some NULLS. How to use those defaults in my insert?
I've tried to get these defaults using defenition from sys.default_constraints, but there are no defaults created as CREATE DEFAULT in sys.default_constraints.
'''SQL
--Code I may not change
CREATE TYPE dt_myType FROM varchar(255) NOT NULL
GO
CREATE DEFAULT myDefault
AS
''
GO
EXEC sp_bindefault 'myDefault', 'dt_myType';
GO
CREATE TABLE myTable (
f1 dt_myType NOT NULL )
GO
--My code
insert into myTable
(f1)
select
case f
when 1 then 'example'
else --I need default here
end
from ...
'''

Answer 1

If you do not have very many columns to test, you could do something like this:
insert into t (<other columns>, a, b)
select <other columns>, x.a, x.b
from x
where x.a is not null and x.b is not null;
insert into t (<other columns>, a )
select <other columns>, x.a
from x
where x.a is not null and x.b is null;
insert into t (<other columns>, b )
select <other columns>, x.b
from x
where x.a is null and x.b is not null;
insert into t (<other columns>)
select <other columns>
from x
where x.a is null and x.b is null;
This doesn't generalize well to many more columns.
Otherwise, here are some options I can think of:
Loop through each record (say using a dreaded cursor) and construct the insert based on the presence of NULL values.
Use an instead of trigger to basically construct the inserts, as described above.
Insert the data so all values are default values and then update them with the values in the data.
Figure out a way to parse the default value in the metadata, represent it as the appropriate type, and include it in your query.