I'm a newbie to SQL and I'm having a real hard time setting up this trigger. It's for a Bank Console JDBC sort of thing.
I have a schema with three entities, USER, ACCOUNT, and TRANSACTION. I want to keep track of all the changes a user makes to one of her accounts by inserting a new row into my transaction entity, which has columns of
id, which I'm handling with a sequence,
user_id (referencing a foreign key stored in the accounts entity),
account_id (referencing the account entity's primary key),
a time stamp, (for which I'm using Oracle's CURRENT_TIMESTAMP function),
and a transaction-type, which is either of 'deposit' or 'withdrawal'.
Here's how my Trigger looks right now.
CREATE OR REPLACE TRIGGER ADD_TX
ON ACCOUNT
AFTER INSERT, UPDATE
REFERENCING OLD AS OLD NEW AS NEW
FOR EACH ROW
DECLARE old_balance number, new_balance number, transaction_type varchar2(100);
BEGIN
transaction_type := CASE WHEN :NEW.balance < :OLD.balance THEN 'WITHDRAWAL' ELSE 'DEPOSIT' END;
INSERT INTO TRANSACTIONS VALUES(TRANSACTION_ID_SEQ.NEXTVAL, :NEW.USER_ID, :NEW.id, CURRENT_TIMESTAMP, :NEW.account_type, transaction_type);
end if;
END;
/
Any guidance would be most appreciated
Something like this might do the job:
CREATE OR REPLACE TRIGGER add_tx AFTER
INSERT OR UPDATE ON account
FOR EACH ROW
BEGIN
INSERT INTO transactions VALUES (
transaction_id_seq.NEXTVAL,
:new.user_id,
:new.id,
current_timestamp,
:new.account_type,
CASE
WHEN :new.balance <:old.balance THEN 'WITHDRAWAL'
ELSE 'DEPOSIT'
END
);
END;
/
Though, I'd suggest you to name ALL columns you're inserting to; the way you wrote it, it is unclear which value goes into which column, and such a code might (and probably will) break, some day.
Related
I am trying to prevent inserts of records into a table for scheduling. If the start date of the class is between the start and end date of a previous record, and that record is the same location as the new record, then it should not be allowed.
I wrote the following trigger, which compiles, but of course mutates, and therefore has issues. I looked into compound triggers to handle this, but either it can't be done, or my understanding is bad, because I couldn't get that to work either. I would have assumed for a compound trigger that I'd want to do these things on before statement, but I only got errors.
I also considered after insert/update, but doesn't that apply after it's already inserted? It feels like that wouldn't be right...plus, same issue with mutation I believe.
The trigger I wrote is:
CREATE OR REPLACE TRIGGER PREVENT_INSERTS
before insert or update on tbl_classes
DECLARE
v_count number;
v_start TBL_CLASS_SCHED.start_date%type;
v_end TBL_CLASS_SCHED.end_date%type;
v_half TBL_CLASS_SCHED.day_is_half%type;
BEGIN
select start_date, end_date, day_is_half
into v_start, v_end, v_half
from tbl_classes
where class_id = :NEW.CLASS_ID
and location_id = :NEW.location_id;
select count(*)
into v_count
from TBL_CLASS_SCHED
where :NEW.START_DATE >= (select start_date
from TBL_CLASS_SCHED
where class_id = :NEW.CLASS_ID
and location_id = :NEW.location_id)
and :NEW.START_DATE <= (select end_date
from TBL_CLASS_SCHED
where class_id = :NEW.CLASS_ID
and location_id = :NEW.location_id);
if (v_count = 2) THEN
RAISE_APPLICATION_ERROR(-20001,'You cannot schedule more than 2 classes that are a half day at the same location');
end if;
if (v_count = 1 and :NEW.day_is_half = 1) THEN
if (v_half != 1) THEN
RAISE_APPLICATION_ERROR(-20001,'You cannot schedule a class during another class''s time period of the same type at the same location');
end if;
end if;
EXCEPTION
WHEN NO_DATA_FOUND THEN
null;
END;
end PREVENT_INSERTS ;
Perhaps it can't be done with a trigger, and I need to do it multiple ways? For now I've done it using the same logic before doing an insert or update directly, but I'd like to put it as a constraint/trigger so that it will always apply (and so I can learn about it).
There are two things you'll need to fix.
Mutating occurs because you are trying to do a SELECT in the row level part of a trigger. Check out COMPOUND triggers as a way to mitigate this. Basically you capture info at row level, and the process that info at the after statement level. Some examples of that in my video here https://youtu.be/EFj0wTfiJTw
Even with the mutating issue resolved, there is a fundamental flaw in the logic here (trigger or otherwise) due to concurrency. All you need is (say) three or four people all using this code at the same time. All of them will get "Yes, your count checks are ok" because none of them can see each others uncommitted data. Thus they all get told they can proceed and when they finally commit, you'll have multiple rows stored hence breaking the rule your tirgger (or wherever your code is run) was trying to enforce. You'll need to look an appropriate row so that you can controlling concurrent access to the table. For an UPDATE, that is easy because this means there is already some row(s) for the location/class pairing. For an INSERT, you'll need to ensure an appropriate unique constraint is in place on a parent table somewhere. Hard to say without seeing the entire model
In principle a compound trigger could be this one:
CREATE OR REPLACE TYPE CLASS_REC AS OBJECT(
CLASS_ID INTEGER,
LOCATION_ID INTEGER,
START_DATE DATE,
END_DATE DATE,
DAY_IS_HALF INTEGER
);
CREATE OR REPLACE TYPE CLASS_TYPE AS TABLE OF CLASS_REC;
CREATE OR REPLACE TRIGGER UIC_CLASSES
FOR INSERT OR UPDATE ON TBL_CLASSES
COMPOUND TRIGGER
classes CLASS_TYPE;
v_count NUMBER;
v_half TBL_CLASS_SCHED.DAY_IS_HALF%TYPE;
BEFORE STATEMENT IS
BEGIN
classes := CLASS_TYPE();
END BEFORE STATEMENT;
BEFORE EACH ROW IS
BEGIN
classes.EXTEND;
classes(classes.LAST) := CLASS_REC(:NEW.CLASS_ID, :NEW.LOCATION_ID, :NEW.START_DATE, :NEW.END_DATE, :NEW.DAY_IS_HALF);
END BEFORE EACH ROW;
AFTER STATEMENT IS
BEGIN
FOR i IN classes.FIRST..classes.LAST LOOP
SELECT COUNT(*), v_half
INTO v_count, v_half
FROM TBL_CLASSES
WHERE CLASS_ID = classes(i).CLASS_ID
AND LOCATION_ID = classes(i).LOCATION_ID
AND classes(i).START_DATE BETWEEN START_DATE AND END_DATE
GROUP BY v_half;
IF v_count = 2 THEN
RAISE_APPLICATION_ERROR(-20001,'You cannot schedule more than 2 classes that are a half day at the same location');
END IF;
IF v_count = 1 AND classes(i).DAY_IS_HALF = 1 THEN
IF v_half != 1 THEN
RAISE_APPLICATION_ERROR(-20001,'You cannot schedule a class during another class''s time period of the same type at the same location');
end if;
end if;
END LOOP;
END AFTER STATEMENT;
END;
/
But as stated by #Connor McDonald, there are several design flaws - even in a single user environment.
A user may update the DAY_IS_HALF, I don't think the procedure covers all variants. Or a user updates END_DATE and by that, the new time intersects with existing classes.
Better avoid direct insert into the table and create a PL/SQL stored procedure in which you perform all the validations you need and then, if none of the validations fail, perform the insert. And grant execute on that procedure to the applications and do not grant applications insert on that table. That is a way to have all the data-related business rules in the database and make sure that no data that violates those rules in entered into the tables, no matter by what client application, for any client application will call a stored procedure to perform insert or update and will not perform DML directly on the table.
I think the main problem is the ambiguity of the role of the table TBL_CLASS_SCHED and the lack of clear definition of the DAY_IS_HALF column (morning, afternoon ?).
If the objective is to avoid 2 reservations of the same location at the same half day, the easiest solution is to use TBL_CLASS_SCHED to enforce the constraint with (start_date, location_id) being the primary key, morning reservation having start_date truncated at 00:00 and afternoon reservation having start_date set at 12:00, and you don't need end_date in that table, since each row represents an half day reservation.
The complete solution will then need a BEFORE trigger on TBL_CLASSES for UPDATE and INSERT events to make sure start_date and end_date being clipped to match the 00:00 and 12:00 rule and an AFTER trigger on INSERT, UPDATE and DELETE where you will calculate all the half-day rows to maintain in TBL_CLASS_SCHED. (So 1 full day reservation in TBL_CLASSES, will generate 2 rows in TBL_CLASS_SCHED). Since you maintain TBL_CLASS_SCHED from triggers set on TBL_CLASSES without any need to SELECT on the later, you don't have to worry about mutating problem, and because you will constraint start_date to be either at 00:00 or 12:00, the primary key constraint will do the job for you. You may even add a unique index on (start_date, classe_id) in TBL_CLASS_SCHED to avoid a classe to be scheduled at 2 locations at the same time, if you need to.
How do i create a condition on oracle db? I'm new on this db.
I already create table called vehicle_parked, but i want to trigger vehicle number as NULL if parkedOnSite value is 'F' and the structure like this
vehicle_parked
- parked_id number(4) PK
- arrivalTime date
- parkedOnSite varchar(1) // value will be T/F
- vehicle_number varchar(8)
Thanks.
you can easily manipulate your data by creating a DML trigger that fires before your data is inserted into table, and changes data.
CREATE OR REPLACE TRIGGER trg_vehicle_parked
BEFORE INSERT OR UPDATE
ON vehicle_parked
FOR EACH ROW
DECLARE
BEGIN
if :new.parkedOnSite = 'F' then
:new.vehicle_number := null;
end if;
END;
/
In triggers, besides :new, we can use :old pseudo codes. They stand for the values of the columns before(:old) or after(:new) DML statements issued.
Especially for an update or delete trigger you may compare your column's old and new values in a trigger as in the example :
if ( nvl(:old.vehicle_number,0) != nvl(:new.vehicle_number,0) ) then
go_on_with_statement ....
I am having problems with this code below, which is a trigger used in Oracle SQL:
CREATE OR REPLACE TRIGGER TRG_TUTOR_BLOCK
BEFORE INSERT OR UPDATE ON tutors
FOR EACH ROW
DECLARE
BEGIN
IF :new.tutorName = :old.tutorName
THEN
RAISE_APPLICATION_ERROR(-20101, 'A tutor with the same name currently exists.');
ROLLBACK;
END IF;
END;
/
This trigger is used to prevent users from entering the same tutor name at different records.
After I insert two records with the same tutorname, the trigger does not block me from inserting it. Is there anyone can tell me what are the problems with this coding? Here are the sample format and insert values:
INSERT INTO tutors VALUES (tutorID, tutorName tutorPhone, tutorAddress, tutorRoom, loginID);
INSERT INTO tutors VALUES ('13SAS01273', 'Tian Wei Hao', '019-8611123','No91, Jalan Wangsa Mega 2, 53100 KL', 'A302', 'TianWH');
Trigger in Kamil's example will throw ORA-04091, you can see this with your own eyes here. ROLLBACK in a trigger is unnecessary, it runs implicitly when a trigger makes a statement to fail.
You can prohibit any DML on table by altering it with read only clause:
alter table tutors read only;
At last, integrity should be declarated with integrity constraints and not with triggers.
Good luck!
You don't need a trigger for this in Oracle.
You can do it with an "unique index" on the tutorName column (see http://docs.oracle.com/cd/B28359_01/server.111/b28310/indexes003.htm#i1106547).
Note: about your trigger, it fails on checking for another record with the same tutorName because it's not scanning the tutors table for another record with the same tutorName, it's just comparing the tutorName values of the row you are creating (in this case, old.tutorName is just NULL, because the row doesn't exist yet).
Check the case in yours trigger body
IF :new.tutorName = :old.tutorName
It returns true only if 'tutorName' value is the same in new and old record. When you'll trying to updat some value you'll get
IF 'someTutorName' = 'someTutorName'
which will return TRUE.
Inserting row cannot fire this rule because you're trying to compare something like that:
'someTutorName' = NULL
This case always returns FALSE.
Try to use something like that
CREATE OR REPLACE TRIGGER TRG_TUTOR_BLOCK
BEFORE INSERT OR UPDATE ON tutors
FOR EACH ROW
DECLARE
rowsCount INTEGER;
BEGIN
SELECT COUNT(*) FROM tutors WHERE tutorName is :new.tutorName INTO rowsCount;
IF rowsCount > 0
THEN
RAISE_APPLICATION_ERROR(-20101, 'A tutor with the same name currently exists.');
ROLLBACK;
END IF;
END;
/
But the best solution is the one mentioned by friol - use unique index by executing SQL like this
ALTER TABLE tutors
ADD CONSTRAINT UNIQUE_TUTOR_NAME UNIQUE (tutorName);
If you wanna completely ignore recording a row to a table you can follow these steps
rename table to something else and create a view with the same name and create an instead of trigger.
create table usermessages (id number(10) not null)
GO
alter table usermessages rename to xusermessages
GO
create or replace view usermessages as (select * from xusermessages)
GO
create or replace trigger usermessages_instead_of_trg
instead of insert or update on usermessages
for each row
begin
Null ;
end ;
GO
insert into usermessages(123)
Live test available here below
http://sqlfiddle.com/#!4/ad6bc/2
I need to set a constraint that the user is unable to enter any records after he/she has entered 5 records in a single month. Would it be advisable that I write a trigger or procedure for that? Else is that any other ways that I can setup the constraint?
Instead of writing a trigger i have opt to write a procedure for the constraint but how do i check if the procedure is working?
Below is the procedure:
CREATE OR REPLACE PROCEDURE InsertReadingCheck
(
newReadNo In Int,
newReadValue In Int,
newReaderID In Int,
newMeterID In Int
)
AS
varRowCount Int;
BEGIN
Select Count(*) INTO varRowCount
From Reading
WHERE ReaderID = newReaderID
AND Trunc(ReadDate,'mm') = Trunc(Sysdate,'mm');
IF (varRowCount >= 5) THEN
BEGIN
DBMS_OUTPUT.PUT_LINE('*************************************************');
DBMS_OUTPUT.PUT_LINE('');
DBMS_OUTPUT.PUT_LINE(' You attempting to enter more than 5 Records ');
DBMS_OUTPUT.PUT_LINE('');
DBMS_OUTPUT.PUT_LINE('*************************************************');
ROLLBACK;
RETURN;
END;
ELSIF (varRowCount < 5) THEN
BEGIN
INSERT INTO Reading
VALUES(seqReadNo.NextVal, sysdate, newReadValue,
newReaderID, newMeterID);
COMMIT;
END;
END IF;
END;
Anyone can help me look through
This is the sort of thing that you should avoid putting in a trigger. Especially the ROLLBACK and the COMMIT. This seems extremely dangerous (and I'm not even sure whether it's possible). You might have other transactions that you wish to commit that you rollback or vice versa.
Also, by putting this in a trigger you are going to get the following error:
ORA-04091: table XXXX is mutating, trigger/function may not see it
There are ways round this but they're excessive and involve doing something funky in order to get round Oracle's insistence that you do the correct thing.
This is the perfect opportunity to use a stored procedure to insert data into your table. You can check the number of current records prior to doing the insert meaning that there is no need to do a ROLLBACK.
It depends upon your application, if insert is already present in your application many times then trigger is better option.
This is a behavior constraint. Its a matter of opinion but I would err on the side of keeping this kind of business logic OUT of your database. I would instead keep track of who added what records in the records table, and on what day/times. You can have a SP to get this information, but then your code behind should handle whether or not the user can see certain links (or functions) based on the data that's returned. Whether that means keeping the user from accessing the page(s) where they insert records, or give them read only views is up to you.
One declarative way you could solve this problem that would obey all concurrency rules is to use a separate table to keep track of number of inserts per user per month:
create table inserts_check (
ReaderID integer not null,
month date not null,
number_of_inserts integer constraint max_number_of_inserts check (number_of_inserts <= 5),
primary key (ReaderID, month)
);
Then create a trigger on the table (or all tables) for which inserts should be capped at 5:
create trigger after insert on <table>
for each row
begin
MERGE INTO inserts_check t
USING (select 5 as ReaderID, trunc(sysdate, 'MM') as month, 1 as number_of_inserts from dual) s
ON (t.ReaderID = s.ReaderID and t.month = s.month)
WHEN MATCHED THEN UPDATE SET t.number_of_inserts = t.number_of_inserts + 1
WHEN NOT MATCHED THEN INSERT (ReaderID, month, number_of_inserts)
VALUES (s.ReaderID, s.month, s.number_of_inserts);
end;
Once the user has made 5 inserts, the constraint max_number_of_inserts will fail.
I want to have an 'updateinfo' table in order to record every update/insert/delete operations on another table.
In oracle I've written this:
CREATE TABLE updateinfo ( rnumber NUMBER(10), tablename VARCHAR2(100 BYTE), action VARCHAR2(100 BYTE), UPDATE_DATE date )
DROP TRIGGER TRI_TABLE;
CREATE OR REPLACE TRIGGER TRI_TABLE
AFTER DELETE OR INSERT OR UPDATE
ON demo
REFERENCING NEW AS NEW OLD AS OLD
FOR EACH ROW
BEGIN
if inserting then
insert into updateinfo(rnumber,tablename,action,update_date ) values(rownum,'demo', 'insert',sysdate);
elsif updating then
insert into updateinfo(rnumber,tablename,action,update_date ) values(rownum,'demo', 'update',sysdate);
elsif deleting then
insert into updateinfo(rnumber,tablename,action,update_date ) values(rownum,'demo', 'delete',sysdate);
end if;
-- EXCEPTION
-- WHEN OTHERS THEN
-- Consider logging the error and then re-raise
-- RAISE;
END TRI_TABLE;
but when checking updateinfo, all rnumber column is zero.
is there anyway to retrieve the correct row number?
The only option is to use primary key column of your "demo" table.
ROWNUM is not what you are looking for, read the explanation.
ROWID looks like a solution, but in fact it isn't, because it shouldn't be stored for a later use.
ROWNUM is not what you think it is. ROWNUM is a counter that has only a meaning within the context of one execution of a statement (i.e. the first resulting row always has rownum=1 etc.). I guess you are looking for ROWID, which identifies a row.