This error occurs correctly?

[Andrey Maximenko. Ukraine]

I try to change the query text without reopening dataset

OraSes.Connected := true;
  ods.SQL.Text := 'select 1 from dual';
  ods.Open;
  ods.SQL.Text := 'select ''a'' from dual';
  ods.Refresh; // Project Project1.exe raised exception class EConvertError with message ''a' is not a valid floating point value'. Process stopped. Use Step or Run to continue.

 

[Marco Kalter]

You can indeed not change the fields when refreshing a dataset. You will need to reopen it so that the field names and types are refreshed as well.

 

[Andrey Maximenko. Ukraine]

ok, thanks