Testing and reacting to NULL values

[Jerbear]

In my table I have a field called closed.
If the case is closed it will contain the date it was closed otherwise it remains empty.
I search my DB for a case finishing my query with

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"and closed is null" 

so it only displays open cases.
My Query also converts the closed date

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convert(varchar(12), closed,103) as closed

However, having executed the query and it returns no results it's possibly one of two things.
Either the case does not exist or the case is closed.
I need to know if this Field had a value so I can pop up a message
to the user to advise them that IT IS a CLOSED case.
I have tried the following two commands without success....

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var IsClosed : String;
IsClosed := DBSearchGrid.DataSource.DataSet.FieldByName('closed').AsString;
If IsClosed <> '' Then ShowMessage('Case is a CLOSED Case');

IsClosed := DBSearchGrid.DataSource.DataSet.Fields.Fields[13].AsString;
If IsClosed <> '' Then ShowMessage('Case is a CLOSED Case');

If I search for a known closed case both commands above return nothing in IsClosed.

I use both of the above in other parts of my code without problem.

Any Ideas....

[ViktorV]

To detect that a field is set to NULL, you should use the IsNull property. For example:

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if MSQuery.FieldByName('closed').IsNull then
  ShowMessage('Value is NULL');

[Jerbear]

Thank you ViKtorV.

That works great, but if the field is NOT NULL then how can I get the actual value of that field
into a variable. The code I used, shown in previous post, does not work on this field but works on all
other fields...

[ViktorV]

The code you provided above should return a correct field value. Please compose a small sample reproducing the described behavior and send it to viktorv*devart*com including scripts for creating database objects, in order for us to be able to answer you in more details.