Insert default value when parameter is null

Christophe,

The default value on a column is only applied if you don't specify the column in the INSERT statement.

Since you're explicitiy listing the column in your insert statement, and explicity setting it to NULL, that's overriding the default value for that column

What you need to do is "if a null is passed into your sproc then don't attempt to insert for that column".

This is a quick and nasty example of how to do that with some dynamic sql.

Create a table with some columns with default values...

CREATE TABLE myTable (
    always VARCHAR(50),
    value1 VARCHAR(50) DEFAULT ('defaultcol1'),
    value2 VARCHAR(50) DEFAULT ('defaultcol2'),
    value3 VARCHAR(50) DEFAULT ('defaultcol3')
)

Create a SPROC that dynamically builds and executes your insert statement based on input params

ALTER PROCEDURE t_insert (
    @always VARCHAR(50),
    @value1 VARCHAR(50) = NULL,
    @value2 VARCHAR(50) = NULL,
    @value3 VARCAHR(50) = NULL
)
AS 
BEGIN
DECLARE @insertpart VARCHAR(500)
DECLARE @valuepart VARCHAR(500)

SET @insertpart = 'INSERT INTO myTable ('
SET @valuepart = 'VALUES ('

    IF @value1 IS NOT NULL
    BEGIN
        SET @insertpart = @insertpart + 'value1,'
        SET @valuepart = @valuepart + '''' + @value1 + ''', '
    END

    IF @value2 IS NOT NULL
    BEGIN
        SET @insertpart = @insertpart + 'value2,'
        SET @valuepart = @valuepart + '''' + @value2 + ''', '
    END

    IF @value3 IS NOT NULL
    BEGIN
        SET @insertpart = @insertpart + 'value3,'
        SET @valuepart = @valuepart + '''' + @value3 + ''', '
    END

    SET @insertpart = @insertpart + 'always) '
    SET @valuepart = @valuepart + + '''' + @always + ''')'

--print @insertpart + @valuepart
EXEC (@insertpart + @valuepart)
END

The following 2 commands should give you an example of what you want as your outputs...

EXEC t_insert 'alwaysvalue'
SELECT * FROM  myTable

EXEC t_insert 'alwaysvalue', 'val1'
SELECT * FROM  myTable

EXEC t_insert 'alwaysvalue', 'val1', 'val2', 'val3'
SELECT * FROM  myTable

I know this is a very convoluted way of doing what you need to do. You could probably equally select the default value from the InformationSchema for the relevant columns but to be honest, I might consider just adding the default value to param at the top of the procedure

Try an if statement ...

if @value is null 
    insert into t (value) values (default)
else
    insert into t (value) values (@value)

As far as I know, the default value is only inserted when you don't specify a value in the insert statement. So, for example, you'd need to do something like the following in a table with three fields (value2 being defaulted)

INSERT INTO t (value1, value3) VALUES ('value1', 'value3')

And then value2 would be defaulted. Maybe someone will chime in on how to accomplish this for a table with a single field.

This is the best I can come up with. It prevents sql injection uses only one insert statement and can ge extended with more case statements.

CREATE PROCEDURE t_insert (     @value varchar(50) = null )
as
DECLARE @sQuery NVARCHAR (MAX);
SET @sQuery = N'
insert into __t (value) values ( '+
CASE WHEN @value IS NULL THEN ' default ' ELSE ' @value ' END +' );';

EXEC sp_executesql 
@stmt = @sQuery, 
@params = N'@value varchar(50)',
@value = @value;

GO

Probably not the most performance friendly way, but you could create a scalar function that pulls from the information schema with the table and column name, and then call that using the isnull logic you tried earlier:

    CREATE FUNCTION GetDefaultValue
    (
        @TableName VARCHAR(200),
        @ColumnName VARCHAR(200)
    )
    RETURNS VARCHAR(200)
    AS
    BEGIN
        -- you'd probably want to have different functions for different data types if
        -- you go this route
    RETURN (SELECT TOP 1 REPLACE(REPLACE(REPLACE(COLUMN_DEFAULT, '(', ''), ')', ''), '''', '') 
            FROM information_schema.columns
            WHERE table_name = @TableName AND column_name = @ColumnName)

    END
    GO

And then call it like this:

INSERT INTO t (value) VALUES ( ISNULL(@value, SELECT dbo.GetDefaultValue('t', 'value') )

Insert default value when parameter is null

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