topic Re: Data loss when concatenate in QlikView

Data loss when concatenate

Mon, 26 Jan 2026 18:19:17 GMT

Hello comunity,

Please help with this problem.

I have 2 qvd files I want to concatenate.

QVD1 fileds:

QVD2 fields:

to concatenate I use:

final:

load * from qvd1.qvd (qvd);

concatenate

load * from qvd2.qvd (qvd);

store final ...

drop final;

The problem is: when I read the final file the year and month flaged as 'P' are null.

I have a QV Dashboard which calls serveral QVDs, and I use qualify and unqualify.

qualify *;

unqualify year, month, productCode, clientCode;

load * from final.qvd (qvd);

load * from final2.qvd (qvd);

load * from final3.qvd (qvd);

...

load * from final10.qvd (qvd);

Notes:

- QVD1 has almost 14M of rows.

- QVD2 has 4100 rows of rows.

Re: Data loss when concatenate

swuehl — Mon, 25 Apr 2016 21:41:52 GMT

If you execute

final:

load * from qvd1.qvd (qvd);

concatenate

load * from qvd2.qvd (qvd);

store final ...

And then check the table, you still see year and month values for flag 'P', right?

If you then

drop final;

and then just reload the final table from QVD:

LOAD * FROM final.qvd (qvd);

You get NULL for year and month when flag = 'P'?

Re: Data loss when concatenate

Mon, 25 Apr 2016 21:44:47 GMT

Hello Swuehl,

Yes, everything you said is happening to me.

Re: Data loss when concatenate

swuehl — Mon, 25 Apr 2016 22:38:39 GMT

Could you maybe upload two small sample QVDs and your script?

Re: Data loss when concatenate

qliksus — Tue, 26 Apr 2016 05:00:20 GMT

Could be a difference in the number of columns between QVD1 and QVD2 as you are using Qualify and Unqualify the same column name might get renamed into a different one and thus showing null onconcatenate . Try loading the 2 QVD's without using the concatenate keyword and Qualify and Unqualify and check the result

Re: Data loss when concatenate

MindaugasBacius — Tue, 26 Apr 2016 05:29:41 GMT

I have made an example that works.

Please check the attachments and the script.

Re: Data loss when concatenate

Tue, 26 Apr 2016 14:52:05 GMT

I was trying to upload a small example (because QVD1 is almost 200MB) using those QVD files, but:

When I create the DB QVW it reads all fields as is, everything looks OK, but in my real DB the 'year' and 'month' fields appears as null when Flag is 'P'. It is a little rare that in one DB (new) works OK, but in my official does not.

I was checking all the field names when concatenate, but all necessary fields have the same name, so they should show in the final's file columns 'year' and 'month'.

I am usign in the Final DB qualify *, and unqualify (some common fields between QVDs) because I read several QVD files. My idea making those unqualified fields KEYS.

Marked line is where I can´t figure out why Año (year) and Mes (month) appear as null when flag is 'P'.

I started my Final BD concatenating all of those QVD files, but the DB was very very...slow showing the information.

Re: Data loss when concatenate

swuehl — Tue, 26 Apr 2016 16:49:02 GMT

This code will not concatenate your tables, are you expecting it to do this?

I must admit I am a little confused with your code and where you are creating your concatenated tables and checking the year field and flag fields.

Re: Data loss when concatenate

Tue, 26 Apr 2016 17:00:35 GMT

No, I am not trying to concatenate.