ลองใช้คำสั่งนี้ครับ
update ovst set vn = substring(vn,1,12) where length(trim(vn))=13
update ovstdiag set vn = substring(vn,1,12) where length(trim(vn))=13
update vn_stat set vn = substring(vn,1,12) where length(trim(vn))=13
update opdscreen set vn = substring(vn,1,12) where length(trim(vn))=13
update opitemrece set vn = substring(vn,1,12) where length(trim(vn))=13
update oapp set vn = substring(vn,1,12) where length(trim(vn))=13