set the null value into default value

in my table field createdon shown in the date time format like 5/5/2011..in this field any of the value null means...it should be display into 1/1/2011


with this regard you can write your database query for your solution..

like while selecting your column with datatime you can write like this..

SELECT isnull(createdon,'01/01/2011') as CreatedOn FROM "YOUR TABLE NAME"

this will check first that that filed is null or not, if it is null then select your value like 01/01/2011 or if it is not null then its value will be your actual value...
for more detail on isnull see this..
<a href="http://msdn.microsoft.com/en-us/library/ms184325.aspx">ISNULL</a>[<a href="http://msdn.microsoft.com/en-us/library/ms184325.aspx" target="_blank" title="New Window">^</a>]
or
<a href="http://www.w3schools.com/sql/sql_isnull.asp">ISNULL2</a>[<a href="http://www.w3schools.com/sql/sql_isnull.asp" target="_blank" title="New Window">^</a>]

OR
You can use a CASE..WHEN in SELECT Query also...
for more detail on CASE..WHEN see This

<a href="http://msdn.microsoft.com/en-us/library/ms181765.aspx">CASE..WHEN</a>[<a href="http://msdn.microsoft.com/en-us/library/ms181765.aspx" target="_blank" title="New Window">^</a>]<br />

<a href="http://www.1keydata.com/sql/sql-case.html">CASE..WHEN 2</a>[<a href="http://www.1keydata.com/sql/sql-case.html" target="_blank" title="New Window">^</a>]<br />

<a href="http://www.java2s.com/Code/SQL/Flow-Control/UseCASEWHENstatementinSELECT.htm">CASE..WHENE 3</a>[<a href="http://www.java2s.com/Code/SQL/Flow-Control/UseCASEWHENstatementinSELECT.htm" target="_blank" title="New Window">^</a>]

Hello friend..
first of all you need to clear you question, means what you want. you want null value in codebehind code or to store null value to your database.
and also put some code, so its good for us to understand your problem.

mean while try this...

in c#

for giving null value its not accept directly, but for this you need to define variable like this.

int a = 0 // valid

int a = null // gives error

//but for assining null to it you need to declare it as

int? a = null //valid

i hope its help to you to solve your problem. if its use full for you please accept as ans and also rate it.

The type DateTime is not a reference type, it cannot be null. Change is into nullable type:

class Something {
    System.DateTime? MyTime {
        get { return fMyTime; }
        set {
            if (value == null)
               fMyTime = defaultTime;
            else
               fMyTime = (System.DateTime)value;
        }
    }
    System.DateTime fMyTime;
    static readonly System.DateTime defaultTime = new System.DateTime(2011, 1, 1);
}

The character '?' after System.DateTime indicates nullable type. See:
http://msdn.microsoft.com/en-us/library/1t3y8s4s.aspx[^],
http://msdn.microsoft.com/en-us/library/system.datetime.aspx[^].

—SA