is it possible append data to a qvd without overwrite all the file ?
Now, i'm loading all the old data from a qvd, downloading new data from a DB, concatenate the 2 source and STORE everything in the same qvd used before to load the old data.
Can i just download the new data from the DB, append in the QVD and than load only the last data ?
i don't know if it is possible or i must load everything, STORE everything and load again the last data.
It is not possible to append data to a QVD. You need to store content of a QVD in a resident table, and concatenate additional data to resident table and finally stored resident table into QVD.
As far as I know you can't just add data to an existing qvd without bringing that old data back within the qvw file. Assuming you are using an incremental load it would be something like:
maxdate:
load max(date) as maxdate
from old.qvd;
let vMaxDate = peek('maxdate',-1,'maxdate');
Data:
load * from currentdatabase where date > vMaxDate;
Concatenate(Data)
load * from old.qvd;
Store Date into old.qvd;
Bit laborious but I haven't used incremental loads for a while ...
Emma, yours way works but i'd like having all the old data in the qvd just in case that i need to analize older data without download everything ( i'm managing a lot of data that take much time in downloading)
The other option is to have data stored in chunks rather than all in one big qvd ... I've done that before when I wanted to limit the size of the qvd files,
So you could have one file per week's worth of data or month or something. Name the qvd's MyDataOct2012 or something then, if you want to load them all in you just do load * from MyData*.qvd
