Question

I am using ADO connection to connect to SQL from Inno setup, I am running some select query which i capture it to a variable, if the select query returns empty rows, it throws “Invalid variant type conversion” error. I am not sure if i can use the VarIsNull option and also how to use it in my code. Please help. Below is the sample code.

ADOCommand := CreateOleObject('ADODB.Command');
 ADOCommand.ActiveConnection := ADOConnection;
 SQLQuery := 'SELECT Name FROM sys.databases where name=''' + DBValue + '''';
 ADOCommand.CommandText := SQLQuery;
 ADOCommand.CommandType := adCmdText;
 ADORecordset := ADOCommand.Execute;
 Name := ADORecordset.Fields(0);

Answer 1

You may check if the returned record set is empty before assigning the value to the Name variable.

A empty recordset will return true for the EOF property just after you open it, in code it may look like this example:

  SQLQuery := 'SELECT Name FROM sys.databases where name=''' + DBValue + '''';
  ADOCommand.CommandText := SQLQuery;
  ADOCommand.CommandType := adCmdText;
  ADORecordset := ADOCommand.Execute;
  if ADORecordset.EOF then
  begin
    MsgBox('No records', mbInformation, mb_Ok);
    exit;
  end
  else begin
    Name := ADORecordset.Fields(0);
    MsgBox('Name ''' + Name + '''.', mbInformation, mb_Ok);
  end;