What's the difference between these two blocks and when to use the first or the second?
Create OR Replace trigger trig_before_insert before insert on Employee For each Row
Begin
DBMS_OUTPUT.PUT_LINE('Inserting');
END;
And
Create OR Replace trigger trig_before_insert before insert on Employee
Begin
DBMS_OUTPUT.PUT_LINE('Inserting');
END;
If you perform an
INSERT INTO EMPLOYEE
SELECT ...
and that SELECT returns 100 rows so that the INSERT inserts 100 rows, your first trigger will execute 100 times, once for each row. In the same situation, your second trigger will execute only once.
You can use a BEFORE INSERT...FOR EACH ROW trigger to change the values that are being inserted by accessing them via the :NEW variable. E.g.,
:new.column_1 := 'a different value';
You cannot do that in a statement level trigger (which is what your 2nd trigger is).
There are also limitations in row level triggers (which is what your 1st trigger is). In particular, you may not SELECT from the trigger's base table (EMPLOYEES in this case), because that table is said to be "mutating". The exact reasons, as I understand them, go back to the core principles of relational databases -- specifically that the results of a statement (like INSERT INTO...SELECT) should not depend on the order in which the rows are processed. There are workarounds to this limitation, however, which are beyond the scope of your original question, I think.
Related
I have a trigger but it's not inserting the records into target table.
create or replace trigger ins_det_trig1
after insert on Table_a
declare
pragma autonomous_transaction;
---
begin
insert into inf_det
select
a.loc_id,
a.genre_id,
to_char(a.emp_date,'yyyy-mm-dd'),
a.san_seq
from Table_b a ,
Table_a b
where
b.emp_date=a.emp_date
and b.genre_id=a.genre_id
and b.san_seq=a.san_seq;
commit;
exception
when others
Rollback;
end;
pls help me on this
First of all the trigger is invalid, so it won't do anything. You are using a variable named v_err that you don't declare.
Then, you are swallowing all exceptions. If something goes wrong, you fill that variable with the error code and then silently end the trigger. Thus you'll never get informed when the trigger fails.
But the main problem is that you are not using the trigger as you should use triggers in Oracle. The trigger is an after row trigger (AFTER INSERT ... FOR EACH ROW) and hence fires once per row on inserts of table_a rows. The values that got inserted in a new row can be accessed with :new, e.g. :new.business_date.
You, however, ignore these values and select from the table instead. But at the moment of your select the table is mutating. Let's say we write an insert statement that inserts two rows. The trigger fires two times. It is left to chance which row gets inserted first. Oracle sees this and when you are inside the trigger and try to select, it tells us that the content of the table is not deterministic, as the other row may already be in the table or not. We get a mutating table exception.
Having said this: It seems you want an after statement trigger. A trigger that fires after the insert of the rows is complete. For this to happen remove the FOR EACH ROW clause and the related REFERENCING clause, too.
create or replace trigger ins_det_trig1
after insert on Table_a
declare
...
begin
...
end;
So I am trying to use triggers to basically set some rules.. If anyone has an ID number lower than 3, he will have to pay only 100 dollars, but if someone has an ID above that, he will have to pay more. I did some research and have been told to use triggers and that triggers are very useful when fetching multiple rows. So I tried doing that but it didn't work. Basically the trigger gets created but then when i try to add values, I get the following error:-
ORA-01422: exact fetch returns more than requested number of rows
ORA-06512: at "S.PRICTICKET", line 6
ORA-04088: error during execution of trigger 'S.PRICTICKET'
here is what i did to make the trigger:-
CREATE OR REPLACE TRIGGER PRICTICKET BEFORE INSERT OR UPDATE OR DELETE ON PAYS FOR EACH ROW ENABLE
DECLARE
V_PRICE PAYS.PRICE%TYPE;
V_ID PAYS.ID%TYPE;
V_NAME PAYS.NAME%TYPE;
BEGIN
SELECT ID,NAME INTO V_ID,V_NAME FROM PAYS;
IF INSERTING AND V_ID<3 THEN
V_PRICE:=100;
INSERT INTO PAYS(ID,NAME,PRICE) VALUES (V_ID,V_NAME,V_PRICE);
ELSIF INSERTING AND V_ID>=3 THEN
V_PRICE:=130;
INSERT INTO PAYS(ID,NAME,PRICE) VALUES (V_ID,V_NAME,V_PRICE);
END IF;
END;
and the thing is, when i execute this code, i actually do get a message saying the trigger has been compiled. but when when i try to insert values into the table by using the following code, i get the error message I mentioned above.
INSERT INTO PAYS(ID,NAME) VALUES (19,'SS');
You're getting the error you specified, ORA-01422, because you're returning more than one row with the following SELECT:
SELECT ID,NAME INTO V_ID,V_NAME FROM PAYS;
You need to restrict the result set. For example, I'll use the :NEW psuedorecord to grab the row's new ID value, which if unique, will restrict the SELECT to one row:
SELECT ID,NAME INTO V_ID,V_NAME FROM PAYS WHERE ID = :NEW.ID;
Here is the Oracle docs on using triggers: https://docs.oracle.com/database/121/TDDDG/tdddg_triggers.htm#TDDDG99934
However, I believe your trigger has other issues, please see my comments and we can discuss.
EDIT: Based on our discussion.
ORA-04088: error during execution of trigger
Using INSERT inside a BEFORE INSERT trigger on the same table will create an infinite loop. Please consider using an AFTER INSERT and change your INSERTS to UPDATES, or an INSTEAD OF INSERT.
Additionally, remove DELETE from the trigger definition. That makes no sense in this context.
Let's begin clearing up a few things. You were told "triggers are very useful when fetching multiple rows" this is, as a general rule and without additional context, false. There are 4 types of DML triggers:
Before Statement - fires 1 time for the statement regardless of the number of rows processed.
Before Row - fires once for each row processed during the statement before old and new values are merged into a single set of values. At this point you are allowed to change the values in the columns.
After Row - fires once for row processed during the statement after merging old and new values into a single set of values. At this point you cannot change the column values.
After statement - fires once for the statement regardless of the number of rows processed.
Keep in mind that the trigger is effectively part of the statement.
A trigger can be fired for Insert, Update, or Delete. But, there is no need to fire on each. In this case as suggested, remove the Delete. But also the Update as your trigger is not doing anything with it. (NOTE: there are compound triggers, but they contain segments for each of the above).
In general a trigger cannot reference the table that it is fired upon. See error ORA-04091.
If you're firing a trigger on an Insert it cannot do an insert into that same table (also see ORA-04091) and even if you get around that the Insert would fire the trigger, creating a recursive and perhaps a never ending loop - that would happen here.
Use :New.column_name and :Old.column_name as appropriate to refer to column values. Do not attempt to select them.
Since you are attempting to determine the value of a column you must use a Before trigger.
So applying this to your trigger the result becomes:
CREATE OR REPLACE TRIGGER PRICTICKET
BEFORE INSERT ON PAYS
FOR EACH ROW ENABLE
BEGIN
if :new.id is not null
if :new.ID<3 then
:new.Price :=100;
else
:new.Price := 130;
end if ;
else
null; -- what should happen here?
end if ;
END PRICTICKET ;
I have a trigger:
create or replace trigger trig
before insert on sistem
for each row
declare
v_orta number;
begin
SELECT v_orta INTO :new.orta_qiymet
FROM sistem;
v_orta:=(:new.riyaziyyat+:new.fizika)/2;
insert into sistem(orta_qiymet)
values(v_orta);
end trig;
When I insert a row:
insert into sistem(riyaziyyat,fizika) values(4,4)
I get an error:
Why am I getting that error?
This is fundamentally not understanding how triggers work. You can't generally select from the table the trigger is against, and a before-insert trigger shouldn't not insert into the same table again - as that would just cause the trigger to fire again, infinitely (until Oracle notices and stops it). You aren't even currently using the v_orta value you're attempting to query.
I suspect you think the trigger is instead of your original insert perhaps, and really you want to set the orta_qiymet value in the newly-inserted row automatically based on the other two columns you have supplied. To do that you don't (and can't) select those values; instead you refer to the :NEW pseudorecord as you are already doing, and then set the third column value in that same pseudorow:
create or replace trigger trig
before insert on sistem
for each row
begin
:new.orta_qiymet := (:new.riyaziyyat + :new.fizika)/2;
end trig;
/
There is a lot of information in the documentation; this is similar to one of the examples.
I have a table which can hold many records for one account: different amounts.
ACCOUNTID | AMOUNT
id1 | 1
id1 | 2
id2 | 3
id2 | 4
Every time a record in this table is inserted/updated/deleted we need to evaluate an overall amount in order to know if we should trigger or not an event (by inserting data into another table). The amount is computed based on the sum of records (per account) present in this table.
The computation of the amount should use new values of the records, but we need also old values in order to check some conditions (e.g. old value was X - new value is Y: if [X<=threshold and Y>threshold] then trigger event by inserting a record into another table).
So in order to compute and trigger the event, we created a trigger on this table. Something like this:
CREATE OR REPLACE TRIGGER <trigger_name>
AFTER INSERT OR UPDATE OR DELETE OF MOUNT ON <table_name>
FOR EACH ROW
DECLARE
BEGIN
1. SELECT SUM(AMOUNT) INTO varSumAmounts FROM <table_name> WHERE accountid = :NEW.accountid;
2. varAmount := stored_procedure(varSumAmounts);
END <trigger_name>;
The issue is that statement 1. throws the following error: 'ORA-04091: table is mutating, trigger/function may not see it'.
We tried the following but without success (same exception/error) to select all records which have rowId different than current rowId:
(SELECT SUM(AMOUNT)
INTO varSumAmounts
FROM <table_name>
WHERE accountId = :NEW.accountid
AND rowid <> :NEW.rowid;)
in order to compute the amount as the sum of amounts of all rows beside current row + the amount of current row (which we have in the context of the trigger).
We searched for other solutions and we found some but I don’t know which of them is better and what is the downside for each of them (although they are somehow similar)
Use compound trigger
http://www.oracle-base.com/articles/9i/mutating-table-exceptions.php
http://asktom.oracle.com/pls/asktom/ASKTOM.download_file?p_file=6551198119097816936
To avoid 'table is mutating' error based on solutions 1&2, I used a combination of compound triggers with global temporary tables.
Now we have a compound trigger which uses some global temporary tables to store relevant data from :OLD and :NEW pseudo records. Basically we do the next things:
CREATE OR REPLACE TRIGGER trigger-name
FOR trigger-action ON table-name
COMPOUND TRIGGER
-------------------
BEFORE STATEMENT IS
BEGIN
-- Delete data from global temporary table (GTT) for which source is this trigger
-- (we use same global temporary tables for multiple triggers).
END BEFORE STATEMENT;
-------------------
AFTER EACH ROW IS
BEGIN
-- Here we have access to :OLD and :NEW objects.
-- :NEW and :OLD objects are defined only inside ROW STATEMENTS.
-- Save relevant data regarding :NEW and :OLD into GTT table to use it later.
END AFTER EACH ROW;
--------------------
AFTER STATEMENT IS
BEGIN
-- In this block DML operations can be made on table-name(the same table on which
--the trigger is created) safely.
-- Table is mutating error will no longer appear because this block is not for EACH ROW specific.
-- But we can't access :OLD and :NEW objects. This is the reason why in 'AFTER EACH ROW' we saved them in GTT.
-- Because previously we saved :OLD and :NEW data, now we can continue with our business logic.
-- if (oldAmount<=threshold && newAmount>threshold) then
-- trigger event by inserting record into another table
END AFTER STATEMENT;
END trigger-name;
/
The global temporary tables used are created with option 'ON COMMIT DELETE ROWS', this way I make sure that data from this table will be cleaned at the end of the transaction.
Yet, this error occurred: 'ORA-14450: attempt to access a transactional temp table already in use'.
The problem is that the application uses distributed transactions and in oracle documentation is mentioned that:
"A variety of internal errors can be reported when using Global Temporary Tables (GTTs) in conjunction with Distributed or XA transactions.
...
Temporary tables are not supported in any distributed, and therefore XA, coordinated transaction.
The safest option is to not use temporary tables within distributed or XA transactions as their use in this context is not officially supported.
...
A global temporary table can be safely used if there is only single branch transaction at the database using it, but if there are loopback database links or XA transactions involving multiple branches, then problems can occur including block corruption as per Bug 5344322.
"
It's worth mentioning that I can't avoid XA transactions or making DML on same table which is the subject of the trigger (fixing the data model is not a feasible solution). I've tried using instead of the global temporary table a trigger variable - a collection (table of objects) but I am not sure regarding this approach. Is it safe regarding distributed transactions?
Which other solutions will be suitable in this case to fix either initial issue: 'ORA-04091: table name is mutating, trigger/function may not see it', or the second one: 'ORA-14450: attempt to access a transactional temp table already in use'?
You should carefuly check that you code doesn't use autonomous transactions to access temporary table data:
SQL> create global temporary table t (x int) on commit delete rows
2 /
SQL> insert into t values(1)
2 /
SQL> declare
2 pragma autonomous_transaction;
3 begin
4 insert into t values(1);
5 commit;
6 end;
7 /
declare
*
error in line 1:
ORA-14450: attempt to access a transactional temp table already in use
ORA-06512: error in line 4
In case you do a DELETE FROM <temp-table-name> in BEFORE STATEMENT and AFTER STATEMENT is should not matter if you GTT is defined with ON COMMIT PRESERVE ROWS or ON COMMIT DELETE ROWS.
In your trigger you can define a RECORD/TABLE variable. This variable you can initialize in BEFORE STATEMENT block and loop over it in BEFORE STATEMENT block.
Would be something like this:
CREATE OR REPLACE TRIGGER TRIGGER-NAME
FOR TRIGGER-action ON TABLE-NAME
COMPOUND TRIGGER
TYPE GTT_RECORD_TYPE IS RECORD (ID NUMBER, price NUMBER, affected_row ROWID);
TYPE GTT_TABLE_TYPE IS TABLE OF GTT_RECORD_TYPE;
GTT_TABLE GTT_TABLE_TYPE;
-------------------
BEFORE STATEMENT IS
BEGIN
GTT_TABLE := GTT_TABLE_TYPE(); -- init the table variable
END BEFORE STATEMENT;
-------------------
AFTER EACH ROW IS
BEGIN
GTT_TABLE.EXTEND;
GTT_TABLE(GTT_TABLE.LAST) := GTT_RECORD_TYPE(:OLD.ID, :OLD.PRICE, :OLD.ROWID);
END AFTER EACH ROW;
--------------------
AFTER STATEMENT IS
BEGIN
FOR i IN GTT_TABLE.FIRST..GTT_TABLE.LAST LOOP
-- do something with values
END LOOP;
END AFTER STATEMENT;
END TRIGGER-NAME;
/
Friend, I have question about cascade trigger.
I have 2 tables, table data that has 3 attributes (id_data, sum, and id_tool), and table tool that has 3 attributes (id_tool, name, sum_total). table data and tool are joined using id_tool.
I want create trigger for update info sum_total. So , if I inserting on table data, sum_total on table tool where tool.id_tool = data.id_tool will updating too.
I create this trigger, but error ora-04090.
create or replace trigger aft_ins_tool
after insert on data
for each row
declare
v_stok number;
v_jum number;
begin
select sum into v_jum
from data
where id_data= :new.id_data;
select sum_total into v_stok
from tool
where id_tool=
(select id_tool
from data
where id_data= :new.id_data);
if inserting then
v_stok := v_stok + v_jum;
update tool
set sum_total=v_stok
where id_tool=
(select id_tool
from data
where id_data= :new.id_data);
end if;
end;
/
please give me opinion.
Thanks.
The ora-04090 indicates that you already have an AFTER INSERT ... FOR EACH ROW trigger on that table. Oracle doesn't like that, because the order in which the triggers fire is unpredictable, which may lead to unpredictable results, and Oracle really doesn't like those.
So, your first step is to merge the two sets of code into a single trigger. Then the real fun begins.
Presumably there is only one row in data matching the current value of id_data (if not your data model is rally messed up and there's no hope for your situation). Anyway, that means the current row already gives you access to the values of :new.sum and :new.id_tool. So you don't need those queries on the data table: removing those selects will remove the possibility of "mutating table" errors.
As a general observation, maintaining aggregate or summary tables like this is generally a bad idea. Usually it is better just to query the information when it is needed. If you really have huge volumes of data then you should use a materialized view to maintain the summary, rather than hand-rolling something.