Adminer php 4.8.1
I have a quey sql that starts with

set @variable=5420;
SELECT
_billing_last_name as cognome, _billing_first_name as nome, _billing_email as email, _billing_cf as CF, _billing_bacb as BACBnum,
...

If I remove the set then the export (to Libreoffice calc) run fine, but if I run as is adminer export a null worksheet.
Exporting to MS Excel I can see 3 characters: 

Is this a query problem or an adminer problem?