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First and foremost, I hope this code isn't on a live server - you're wide open to SQL injection in many, many places. That having been said, there's also some suspect logic - for instance, line 186. Even if it were working I'm not sure you'd be getting the results you expect. Right before that, you set $stok_awal to the value of $data['qty'] or 0 if $data['qty'] is null. You then subtract $data['qty'] from $stok_awal (which again, is the value of $data['qty'] or 0) without checking to make sure that $data['qty'] exists. The basic problem here is that $data['qty'] doesn't exist. Or more to the point, $data is null. You need to output $data and see what exactly - if anything - it contains. After that, look into prepared statements and update all your queries.