Insert NULL with ADO from Delphi to SQL Server 2000

Question

I am trying to insert data into a SQL Server 2000 database with the help of ADO in Delphi 2007.

So far I've written something like this:

insert into (a,b)
select :a,:b

qry.parameters.parambyname('a').value := '';
qry.parameters.parambyname('b').value := '';

The error I get is:

Disallowed implicit conversion from data type text to data type nvarchar...
use the convert function to run this query.

The columns in the table allow NULL values.

What I want is that the SQL Server table shows NULL where the value is ''. How can I achieve that?

Answer 1

you can replace with theses lines

qry.parameters.parambyname('a').value := Null;
qry.parameters.parambyname('b').value := Null;

Answer 2

qry.parameters.parambyname('a').value := unassigned;