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Mutating table and recursive SQL errors with trigger

A table 'Tempinst ' with two columns:
a varchar2 (20);
b date ;

We insert a value for 'A' to tempinst table by insert statments in SQL Plus. A trigger has been written to insert/update value for B column by insert or update statement.

Create or replace  trigger dt_update_trig
after insert or update on tempinst
for each row
if inserting then
insert into tempinst (b) values (sysdate);
update tempinst set b = sysdate;
end if;
I have met some errors:
1. Mutating table
2. Recursive SQL error.

Please give me the solution to solve the problem.

The reason you are getting these errors is that you are attempting to insert or update into the same table that has caused the trigger to fire. You can simply change your trigger as follows to fix the problem:

create or replace  trigger dt_update_trig
before insert or update on tempinst
for each row
   :new.b := sysdate ;
First you make the trigger a BEFORE trigger instead of an after trigger. This allows you to use the :new attribute to modify column values before the actual insert or update occurs. And since you want to do the same thing (make column b = sysdate), regardless of whether you insert or update, you can remove the IF statement and just set column b = sysdate.

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