Question

I’d like to use the column’s default value in an stored procedure insert, so that I don’t have to repeat the default value in multiple places (it could change… DRY principle).

The T-SQL INSERT operation has a handy ‘default’ keyword that I can use as follows:

Declare @newA varchar(10)
Set @newA = 'Foo2'

-- I can use "default" like so...
Insert into Table_1 (
    A, 
    B) 
Values (
    @newA, 
    default)

However, If I need to do something conditional, I can’t seem to get the case statement to return ‘default’.

-- How do I use 'default' in a case statement? 
INSERT INTO Table_1 (
    A,
    B )
VALUES (
    @newA,
    CASE WHEN (@newA <> 'Foo2') THEN 'bar' ELSE default END)
-- > yeilds "Incorrect syntax near the keyword 'default'."

I could insert the default, and then update as needed like so:

INSERT INTO Table_1 (
    A,
    B )
VALUES (
    @newA,
    default)
UPDATE Table_1 
SET B = CASE WHEN (A <> 'Foo2') THEN 'bar' ELSE B END
WHERE ID = SCOPE_IDENTITY()

But I’d really like somebody to tell me “There’s a better way…”

Here’s a table definition for this example if it helps…

CREATE TABLE dbo.Table_1 (
    ID int NOT NULL IDENTITY (1, 1),
    A varchar(10) NULL,
    B varchar(10) NULL  )  
GO
ALTER TABLE dbo.Table_1 ADD CONSTRAINT DF_Table_1_A DEFAULT 'A-Def' FOR A
GO
ALTER TABLE dbo.Table_1 ADD CONSTRAINT DF_Table_1_B DEFAULT 'B-Def' FOR B
GO

Answer 1

default only works from within a VALUES() block, which does not seem to be an acceptable value in a CASE statement; you could use an if statement to determine what to insert:

DECLARE @newA varchar(10) = 'Foo2'

IF (@newA <> 'Foo2')
BEGIN
   INSERT INTO Table_1 (A, B)
   SELECT @newA, 'bar'
END
ELSE
BEGIN
   --If you are using default values, you do not have to specify the column
   INSERT INTO Table_1 (A) 
   SELECT @newA
END

I think this is better than updating after an insert, so that you only insert correct data into your table. It also keeps the number of INSERTS/UPDATES to 1. You should also be careful when you using @@IDENTITY due to scoping. Consider looking into SCOPE_IDENTITY().