I would like to run a report in which I could trace all the books/barcodes that haven't been checked-in, in a specific period.

It sounds like you're looking for an inventory report. There are some on the wiki: https://wiki.koha-community.org/wiki/SQL_Reports_Library#Inventory.2F_Shelfl... Adapting "Inventory report" (https://wiki.koha-community.org/wiki/SQL_Reports_Library#Inventory_Report) might give you what you want: SELECT b.title, i.barcode, i.itemcallnumber, i.itemlost, i.damaged, i.datelastseen FROM biblio b LEFT JOIN items i USING (biblionumber) WHERE i.onloan IS NULL AND datelastseen < <<Last seen before (yyyy-mm-dd)|date>> AND i.homebranch=<<Home branch|branches>> ORDER BY datelastseen DESC, i.itemcallnumber ASC -- Owen -- Web Developer Athens County Public Libraries https://www.myacpl.org