Oracle Trigger To Check Values On Insert & Update - oracle

Question

I am trying to check a value-gap crossed with each other or not. Let me explain with a quick scenario.
Rec 1 : Company AA : Distance Gap -> 100 - 200
Rec 2 : Company AA : Distance Gap -> 200 - 300 VALID
Rec 3 : Company AA : Distance Gap -> 250 - 450 INVALID
Rec 4 : Company JL : Distance Gap -> 250 - 450 VALID
Rec 3 Invalid because it is between REC 2's distance values.
Rec 4 Valid because company is different
Thus I wrote a trigger to prevent it.
create or replace trigger ab_redemption_billing_mpr
after insert or update on redemption_billing_mpr
for each row
declare
v_is_distance_range_valid boolean;
begin
v_is_distance_range_valid := p_redemption_billing.is_distance_range_valid(:new.id,
:new.redemption_billing_company,
:new.distance_min,
:new.distance_max,
'redemption_billing_mpr');
if not v_is_distance_range_valid then
raise_application_error(-20001, 'This is a custom error');
end if;
end ab_redemption_billing_mpr;
FUNCTION:
function is_distance_range_valid(p_id in number,
p_company in varchar2,
p_distance_min in number,
p_distance_max in number,
p_table_name in varchar2) return boolean is
d_record_number number;
begin
execute immediate 'select count(*) from ' || p_table_name || ' r
where r.redemption_billing_company = :1
and (:2 between r.distance_min and r.distance_max or :3 between r.distance_min and r.distance_max)
and r.id = nvl(:4, id)'
into d_record_number
using p_company, p_distance_min, p_distance_max, p_id;
if (d_record_number > 0) then
return false;
else
return true;
end if;
end;
is_distance_range_valid() works just as I expected. If it returns false, that means range check is not valid and don't insert or update.
When I create a scenario to catch this exception, oracle gives
ORA-04091: table name is mutating, trigger/function may not see it
and it points select count(*) line when I click debug button.
I don't know why I am getting this error. Thanks in advance.

Answer 1

Just check whether the below approach resolves your issue
Create a log table with columns required for finding the is_distance_range_valid validation and In your trigger insert into this log tab.The trigger on main table has to be a before insert or update trigger
Create a trigger on this log table and do the validation in the log table trigger and raise error.The trigger on log table has to be an after insert or update trigger.
Also this will only work if the row is already existing in the main table and it is not part of the current insert or update. If validation of the current insert or update is required then we need to use the :new.column_name to do the validation
Test:-
create table t_trg( n number);
create table t_trg_log( n number);
create or replace trigger trg_t
before insert or update on t_trg
for each row
declare
l_cnt number;
begin
insert into t_trg_log values(:new.n);
end trg_t;
create or replace trigger trg_t_log
after insert or update on t_trg_log
for each row
declare
l_cnt number;
begin
select count(1) into l_cnt from t_trg
where n=:new.n;
if l_cnt > 0 then
raise_application_error(-20001, 'This is a custom error');
end if;
end trg_t_log;
The first time I insert it doesn't throw error
insert into t_trg values(7);
1 row inserted.
The second time I execute, I get the custom error
insert into t_trg values(7);
Error report -
ORA-20001: This is a custom error
ORA-06512: at "TRG_T_LOG", line 7
ORA-04088: error during execution of trigger 'TRG_T_LOG'
ORA-06512: at "TRG_T", line 4
ORA-04088: error during execution of trigger 'TRG_T'
Update:-Using compound trigger the error is thrown in the first time the insert is done since it also takes into account the current row that we are updating or inserting while doing the SELECT

Answer 2

First I want to thanks to psaraj12 for his effort.
I found solution. Oracle forces us to not use select query before each row.
Oracle trigger error ORA-04091
So I wrote this and it works.
create or replace trigger ab_redemption_billing_mpr
for insert or update on redemption_billing_mpr
compound trigger
v_is_distance_range_valid boolean;
id redemption_billing_mpr.id%type;
redemption_billing_company redemption_billing_mpr.redemption_billing_company%type;
distance_min redemption_billing_mpr.distance_min%type;
distance_max redemption_billing_mpr.distance_max%type;
after each row is
begin
id := :new.id;
redemption_billing_company := :new.redemption_billing_company;
distance_min := :new.distance_min;
distance_max := :new.distance_max;
end after each row;
after statement is
begin
v_is_distance_range_valid := p_redemption_billing.is_distance_range_valid(id,
redemption_billing_company,
distance_min,
distance_max,
'redemption_billing_mpr');
if not v_is_distance_range_valid then
raise_application_error(-20001, 'This is a custom error');
end if;
end after statement;
end ab_redemption_billing_mpr;
We must use compound trigger to deal with it.