Hopefully this is the last of many questions about triggers! Still working with the same database where the Order_line entity is a link entity between Order and Products. With this trigger I just want to check if the current order quantity is greater than the stock in Products. At the moment I would be doing this by using two variables, Ordered(quantity) and Total(Stock) and comparing them, but this isn't working.
If the quantity is greater than the stock the record being inserted must be deleted and an error is raised.
CREATE OR REPLACE TRIGGER Checks_Order
BEFORE INSERT ON order_line
FOR EACH ROW
DECLARE
ordered int;
total INT;
BEGIN
SELECT ol.quantity INTO ordered FROM order_line ol WHERE
ol.product_no = :new.product_no;
if(ordered>0) then
SELECT p.stock INTO total FROM
products p WHERE p.product_no = :new.product_no;
IF (ordered < total) then
DELETE FROM order_line ol where ol.order_no = :new.order_no;
RAISE_APPLICATION_ERROR(-20103, 'Not enough stock!');
END IF;
END IF;
END;
.
run
Help, please?
The trigger will not work because you cannot select or even delete from the table that the trigger belongs to.
But you don't need to actually, the value that is ordered can be obtained through :new.quantity.
And if you raise an error, the INSERT will not happen, no need to DELETE the row.
So - assuming I understood your intention correctly - the following should do what you want:
CREATE OR REPLACE TRIGGER Checks_Order
BEFORE INSERT ON order_line
FOR EACH ROW
DECLARE
total INT;
BEGIN
if (:new.quantity > 0) then
SELECT p.stock
INTO total
FROM products p
WHERE p.product_no = :new.product_no;
IF (:new.quantity > total) then
RAISE_APPLICATION_ERROR(-20103, 'Not enough stock!');
END IF;
END IF;
END;
/
Btw: I guess you want :new.quantity > total not < total
Related
create table file( member_no number, filepath varchar2(100) );
I want to limit the number of duplicate rows of member_no in this table.
for example:
In this way, the number of member_no can be up to 5, but it shouldn't be more than six.
how can I do this?
So you have two ways I can think of:
when you are inserting (i assume you are using a store procedure) run an if to check the current rows
Declare
count number;
too_many_num_exception EXCEPTION;
BEGIN
select count(file_path) into count from file where member_no = <num_you_are_inserting>;
if(count = 5)
Then
raise too_many_num_exception;
end if;
insert(...);
EXCEPTION
WHEN too_many_num_exception then
--do something
end;
or you could try play around with creating indexes on you tables (however this may not work - it's just a thought)
CREATE UNIQUE INDEX file_ix1 on file (
CASE WHEN (select count() from file ... ) < 6 THEN member_id ELSE NULL END)
online
Although im not 100% if that would work
I am relatively new to PL/SQL and i am trying to create a trigger that will alert me after an UPDATE on a table Review. When it is updated I want to ge the username(User table), score(Review Table), and product name (Product Table) and print them out:
This is what I have so far:
three tables:
Review: score, userid,pid, rid
Users: userid,uname
Product: pid,pname
So Review can reference the other tables with forigen keys.
create or replace trigger userNameTrigger
after insert on review
for each row
declare
x varchar(256);
y varchar(256);
z varchar(256);
begin
select uname into x , pname into y , score into z
from review r , product p , users u
where r.pid = p.pid and r.userid = u.userid and r.rid =new.rid;
dbms_output.put_line('user: '|| X||'entered a new review for Product: '|| Y || 'with a review score of: '|| Z);
end;
The problem I am having is I cannot seem to figure out how to store the selected fields into the variables and output it correctly.
DDL:
Create Table Review
(
score varchar2(100)
, userid varchar2(100)
, pid varchar2(100)
, rid varchar2(100)
);
Create Table Users
(
userid varchar2(100)
, uname varchar2(100)
);
Create Table Product
(
pid varchar2(100)
, pname varchar2(100)
);
The first problem I can see is that you're missing a colon when you refer to new.rid. The second is that you're accessing the review table inside a row-level trigger on that same table, which will give you a mutating table error at some point; but you don't need to as all the data from the inserted row is in the new pseudorow.
create or replace trigger userNameTrigger
after insert on review
for each row
declare
l_uname users.uname%type;
l_pname product.pname%type;
begin
select u.uname into l_uname
from users u
where u.userid = :new.userid;
select p.pname
into l_pname
from product
where p.pid = :new.pid;
dbms_output.put_line('user '|| l_uname
|| ' entered a new review for product ' || l_pname
|| ' with a review score of '|| :new.score);
end;
The bigger problem is that the only person who could see the message is the user inserting tow row, which seems a bit pointless; and they would have to have output enabled in their session to see it.
If you're trying to log that so someone else can see it then store it in a table or write it to a file. As the review table can be queried anyway it seems a bit redundant though.
Having all your table columns as strings is also not good - don't store numeric values (e.g. scores, and probably the ID fields) or dates as strings, use the correct data types. It will save you a lot of pain later. You also don't seem to have any referential integrity (primary/foreign key) constraints - so you can review a product that doesn't exist, for instance, which will cause a no-data-found exception in the trigger.
It makes really no sense to use a trigger to notify themselves about changed rows. If you insert new rows into the table, then you have all info about them. Why not something like the block below instead a trigger:
create table reviews as select 0 as rid, 0 as userid, 0 as score, 0 as pid from dual where 1=0;
create table users as select 101 as userid, cast('nobody' as varchar2(100)) as uname from dual;
create table products as select 1001 as pid, cast('prod 1001' as varchar2(100)) as pname from dual;
<<my>>declare newreview reviews%rowtype; uname users.uname%type; pname products.pname%type; begin
insert into reviews values(1,101,10,1001) returning rid,userid,score,pid into newreview;
select uname, pname into my.uname, my.pname
from users u natural join products p
where u.userid = newreview.userid and p.pid = newreview.pid
;
dbms_output.put_line('user: '||my.uname||' entered a new review for Product: '||my.pname||' with a review score of: '||newreview.score);
end;
/
output: user: nobody entered a new review for Product: prod 1001 with a review score of: 10
In order to inform another session about an event you should use dbms_alert (transactional) or dbms_pipe (non transactional) packages. An example of dbms_alert:
create or replace trigger new_review_trig after insert on reviews for each row
begin
dbms_alert.signal('new_review_alert', 'signal on last rid='||:new.rid);
end;
/
Run the following block in another session (new window, worksheet, sqlplus or whatever else). It will be blocked until the registered signal is arrived:
<<observer>>declare message varchar2(400); status integer; uname users.uname%type; pname products.pname%type; score reviews.score%type;
begin
dbms_alert.register('new_review_alert');
dbms_alert.waitone('new_review_alert', observer.message, observer.status);
if status != 0 then raise_application_error(-20001, 'observer: wait on new_review_alert error'); end if;
select uname, pname, score into observer.uname, observer.pname, observer.score
from reviews join users using(userid) join products using (pid)
where rid = regexp_substr(observer.message, '\w+\s?rid=(\d+)', 1,1,null,1)
;
dbms_output.put_line('observer: new_review_alert for user='||observer.uname||',product='||observer.pname||': score='||observer.score);
end;
/
Now in your session:
insert into reviews values(2, 101,7,1001);
commit; --no alerting before commit
The another (observer) session will be finished with the output:
observer: new_review_alert for user=nobody,product=prod 1001: score=7
P.S. There was no RID in the Table REVIEW, so i'll just assume it was supposed to be PID.
create or replace trigger userNameTrigger
after insert on review
for each row
declare
x varchar2(256);
y varchar2(256);
z varchar2(256);
BEGIN
select uname
, pname
, score
INTO x
, y
, z
from review r
, product p
, users u
where r.pid = p.pid
and r.userid = u.userid
and r.PID = :new.pid;
dbms_output.put_line('user: '|| X ||'entered a new review for Product: '|| Y || 'with a review score of: '|| Z);
end userNameTrigger;
You just made a mistake on the INTO statement, you can just clump them together in one INTO.
New to working with PL/SQL and trying to create a statement level trigger that will change the 'Reorder' value to 'Yes' when the product quantity (p_qoh) is either less than 10 or less than two times the product minimum (p_min). And if that's not the case, then to change the 'Reorder' value to 'No'. My problem is that when I perform an update for a specific product, it changes the reorder value of all rows instead of the one I'm specifying. Can't seem to figure out where I'm going wrong, think I've been staring at it too long, any help is greatly appreciated.
CREATE OR REPLACE TRIGGER TRG_AlterProd
AFTER INSERT OR UPDATE OF p_qoh, p_min ON product
DECLARE
v_p_min product.p_min%type;
v_p_qoh product.p_qoh%type;
CURSOR v_cursor IS SELECT p_min, p_qoh FROM product;
BEGIN
OPEN v_cursor;
LOOP
FETCH v_cursor INTO v_p_min, v_p_qoh;
EXIT WHEN v_cursor%NOTFOUND;
IF v_p_qoh < (v_p_min * 2) OR v_p_qoh < 10 THEN
UPDATE product SET p_reorder = 'Yes';
ELSE
UPDATE product SET p_reorder = 'No';
END IF;
END LOOP;
END;
/
The update command :
UPDATE product SET p_reorder = 'Yes';
updates all of your rows because you are not specifying a WHERE clause.
What you can do is to retrieve the product's id (product_id) using your cursor and save it so that you would use it this way:
UPDATE product SET p_reorder = 'Yes' WHERE id = product_id;
Whoaa, this is not how you do triggers.
1 - Read the Oracle Trigger Documentation
2 - (almost) Never do a commit in a trigger. That is the domain of the calling application.
3 - There is no need to select anything related to product. You already have the product record at hand with the :new and :old pseudo records. Just update the column value in :new as needed. Example below (not checked for syntax errors, etc.);
CREATE OR REPLACE TRIGGER TRG_AlterProd
BEFORE INSERT OR UPDATE OF p_qoh, p_min ON product
FOR EACH ROW
BEGIN
IF :new.p_qoh < (:new.p_min * 2) OR :new.p_qoh < 10 THEN
:new.p_reorder = 'Yes';
ELSE
:new p_reorder = 'No';
END IF;
END;
#StevieP, If you need to commit inside a trigger, you may want to consider doing it as Autonomous Transaction.
Also, sorry if my understanding of your problem statement is wrong, but your it sounded to me like a row level trigger - are you only updating the current row or are you scanning the entire table to change status on several rows? If it's on current row, #OldProgrammer's solution seems right.
And I am just curious, if you do an UPDATE statement inside the trigger on the same table, wouldn't it generate (recursive) trigger(s)? I haven't done statement triggers like this, so sorry if this is not the expected trigger behavior.
To me a statement trigger would make more sense, if the trigger was on say, sales table, when a product is sold (inserted into sales table), it will trigger the corresponding product id records to be updated (to REORDER) in Product table. That will prevent recursion danger also.
I've been trying to implement this trigger for a while now and am making progress (I think!) but now I am getting a mutation error.
What I have here is three entities (that are relevant here), Customer_Order(total etc), Order_Line(quantity, subtotal etc) and Products(stock, price). Order_line is a link entity and so a product can be in many order_lines and a customer_order can have many order_lines, but an order_line can only appear once in an order and can only contain one product. The purpose of the trigger is to take the subtotal from order_line(or price from products I think actually) and the quantity from order_line, multiply them and update the new order_line's subtotal.
So I insert an order_line with my product foreign key, quantity of 3 and price of 4.00, the trigger multiplies the two to equal 12 and updates the subtotal. Now, I am thinking it's right to use price here instead of Order_line's subtotal in order to fix the mutation error (which occurs because I am asking the trigger to update the table which is being accessed by the triggering statement, right?), but how do I fix the quantity issue? Quantity won't always be the same value as stock, it has to be less than or equal to stock, so does anyone know how I can fix this to select from product and update order_line? Thanks.
CREATE OR REPLACE TRIGGER create_subtotal
BEFORE INSERT OR UPDATE ON Order_Line
for each row
DECLARE
currentSubTotal order_line.subtotal%type;
currentQuantity order_line.quantity%type;
BEGIN
select order_line.subtotal,order_line.quantity
into currentSubTotal,currentQuantity
from order_line
where product_no = :new.product_no;
IF (currentquantity>-1 ) then
update order_line set subtotal= currentSubTotal * currentQuantity where line_no=:new.line_no;
END IF;
END;
.
run
EDIT: I think I could use the :new syntax to use the quantity value from the triggering statement. I'll try this but I'd appreciate confirmation and help still, thanks.
It sounds like you want something like
CREATE OR REPLACE TRIGGER create_subtotal
BEFORE INSERT OR UPDATE ON order_line
FOR EACH ROW
DECLARE
l_price products.price%type;
BEGIN
SELECT price
INTO l_price
FROM products
WHERE product_no = :new.product_no;
IF( :new.quantity > -1 )
THEN
:new.subtotal := :new.quantity * l_price;
END IF;
END;
If this is something other than homework, however, it doesn't really make sense to pull the price from the PRODUCTS table in this trigger. Presumably, a product's price will change over time. But the price is fixed for a particular order when the order is placed. If the trigger was only defined on INSERT, it would probably be reasonable to just fetch the current price. But if you want to recalculate the subtotal of the line when a row is updated, you'd need to fetch the price as of the time the order was placed (and that assumes that you don't charge different customers different prices at the same time).
From a normalization standpoint, it also tends not to make sense to store calculated fields in the first place. It would make more sense to store the quantity and the price in the order_line table and then calculate the subtotal for the line in a view (or, if you're using 11g, as a virtual column in the table).
The mutation error does not occur because you are updating the table; it occurs because you are querying from the table that is already being updated.
If I'm understanding correctly what you want to do:
CREATE OR REPLACE TRIGGER create_subtotal
BEFORE INSERT OR UPDATE ON Order_Line
for each row
DECLARE
currentPrice products.price%TYPE;
BEGIN
-- Get the current price for the product
SELECT price INTO currentPrice FROM products WHERE product_no = :new.product_no;
-- Set the new subtotal to the current price multiplied by the order quantity
:new.subtotal := currentPrice * :new.quantity;
END;
/
(I'm unclear why you have a test for a quantity below 0, and what you want to occur in this case. If you want to set the subtotal to NULL or 0 in this case, it should be quite easy to modify the above.)
CREATE OR REPLACE TRIGGER "DISC_CLIENT"
BEFORE INSERT ON "PURCHASE"
FOR EACH ROW
DECLARE
checkclient PURCHASE.CLIENTNO%TYPE;
BEGIN
SELECT Clientno INTO checkclient
FROM PURCHASE
GROUP BY ClientNo
HAVING SUM(Amount)=(SELECT MAX(SUM(Amount)) FROM PURCHASE GROUP BY Clientno);
IF :new.ClientNo = checkclient
new.Amount := (:old.Amount * 0.90);
END IF;
END;
/
Seem to be having a problem with this trigger. I know there I cant use the WHEN() clause for subqueries so im hoping this would work but it doesnt! Ideas anyone? :/
Basically im trying to get this trigger to apply a discount to the amount value before inserting if the client matches the top client! : )
There's a non-pretty but easy way round this, create a view and update that. You can then explicitly state all the columns in your trigger and put them in the table. You'd also be much better off creating a 1 row 2 column table, max_amount and then inserting the maximum amount and clientno into that each time. You should also really have a discounted amount column in the purchase table, as you ought to know who you've given discounts to. The amount charged is then amount - discount. This get's around both the mutating table and being unable to update :new.amount as well as making your queries much, much faster. As it stands you don't actually apply a discount if the current transaction is the highest, only if the client has placed the previous highest, so I've written it like that.
create or replace view purchase_view as
select *
from purchase;
CREATE OR REPLACE TRIGGER TR_PURCHASE_INSERT
BEFORE INSERT ON PURCHASE_VIEW
FOR EACH ROW
DECLARE
checkclient max_amount.clientno%type;
checkamount max_amount.amount%type;
discount purchase.discount%type;
BEGIN
SELECT clientno, amount
INTO checkclient, checkamount
FROM max_amount;
IF :new.clientno = checkclient then
discount := 0.1 * :new.amount;
ELSIF :new.amount > checkamount then
update max_amount
set clientno = :new.clientno
, maxamount = :new.amount
;
END IF;
-- Don-t specify columns so it breaks if you change
-- the table and not the trigger
insert into purchase
values ( :new.clientno
, :new.amount
, discount
, :new.other_column );
END TR_PURCHASE_INSERT;
/
As I remember a trigger can't select from a table it's fired for.
Otherwise you'll get ORA-04091: table XXXX is mutating, trigger/function may not see it. Tom advises us not to put too much logic into triggers.
And if I understand your query, it should be like this:
SELECT Clientno INTO checkclient
FROM PURCHASE
GROUP BY ClientNo
HAVING SUM(Amount)=(select max (sum_amount) from (SELECT SUM(Amount) as sum_amount FROM PURCHASE GROUP BY Clientno));
This way it will return the client who spent the most money.
But I think it's better to do it this way:
select ClientNo
from (
select ClientNo, sum (Amount) as sum_amount
from PURCHASE
group by ClientNo)
order by sum_amount
where rownum