Getting ORA-00001 unique constraint violated error when calling a trigger - oracle

Question

create or replace TRIGGER "DB"."TRIG_PERIOD_TRUANCY_INS_UPD"
AFTER UPDATE OR INSERT
ON AT_PERIOD_ATTENDANCE_RECORDS
REFERENCING OLD AS OLD NEW AS NEW
FOR EACH ROW
BEGIN
IF UPDATING THEN
delete at_period_truancy where period_attendance_records_id = :old.period_attendance_records_id;
END IF;
insert into at_period_truancy (period_attendance_records_id, district_number, school_id, student_id, calendar_date, school_year, minutes)
select :new.period_attendance_records_id, :new.district_number, :new.school_id, :new.student_id, :new.calendar_date, :new.school_year,
(case when :new.attendance_status = 'A' then period.end_time - period.begin_time
when coalesce(:new.tardy_time_in_time, period.begin_time) - period.begin_time >
period.end_time - coalesce(:new.tardy_time_out_time, period.end_time)
then coalesce(:new.tardy_time_in_time, period.begin_time) - period.begin_time
else period.end_time - coalesce(:new.tardy_time_out_time, period.end_time) end)*24*60
from ca_calendar cal
inner join ca_school_calendar calendar
on (cal.district_number = calendar.district_number
and cal.calendar_id = calendar.calendar_id )
inner join sc_class_meeting_pattern meeting
on (calendar.cycle_day_cd = meeting.cycle_day_cd)
inner join sc_class class
on (class.school_scheduling_param_id = meeting.school_scheduling_param_id
and class.class_id = meeting.class_id)
inner join sc_period_info period
on (meeting.school_scheduling_param_id = period.school_scheduling_param_id
and meeting.period = period.period)
where :new.district_number = cal.district_number
and cal.is_active_ind = 1
and :new.school_id = cal.school_id
and :new.school_year = cal.school_year
and :new.calendar_type_cd = cal.calendar_type_cd
and :new.track_number = cal.track_number
and :new.calendar_date = calendar.calendar_date
and :new.school_id = class.school_id
and :new.class_id = class.class_id
and 1 in (select use_in_truancy_report_ind
from enum_at_absence_reason_code
where district_number = :new.district_number
and school_id = :new.school_id
and value = :new.absence_reason_code
union all
select use_in_truancy_report_ind
from enum_at_tardy_reason_code
where district_number = :new.district_number
and school_id = :new.school_id
and value = :new.tardy_reason_code);
END TRIG_PERIOD_TRUANCY_INS_UPD;
This is the trigger that I am using. When calling the update statement this trigger is getting invoked and when I pass tardy_reason_code as UN this error is happening. It executes without any issues if I pass tardy_reason_code with different values.

Answer 1

Trigger is inserting into at_period_truancy tables.
As Oracle raises ORA-00001 (unique constraint violated), it means that you're trying to insert primary key value which already exists in the table.
You didn't post create table statement so it is difficult to guess which columns make the primary key, but - you should know it so check which values you already have in there, compare that to values currently being inserted and you'll know what to do.
Maybe you'll have to modify primary key (add other columns? Abandon idea of current primary key and using a sequence (or identity column)) or the way you're inserting values into the table.