I am trying to build an order system that is able to insert a compound order that consists of multiple items and amounts. My database layout is as follows: I have an order table, containing an autoincrement id, item_id, amount and order_group_id columns. I also have an order_group table containing an autoincrement id and a person_id column. The idea is that when a person orders, one new order_group entry is created, and its id is used as the fk in the orders that the person has done.
I presume that this would normally be done in the code of the application. However, I am using postgrest to provide an API for me, which suggests creating a custom view to insert compound entries via that route. This is described here.
This is what I have so far:
CREATE FUNCTION kzc.new_order()
RETURNS TRIGGER
LANGUAGE plpgsql
AS $$
DECLARE
group_id int;
BEGIN
INSERT INTO kzc.order_group (person) VALUES (new.person) RETURNING id AS group_id;
INSERT INTO kzc."order" (item, amount, order_group) VALUES (new.item_id, new.amount, group_id);
RETURN new;
END;
$$;
CREATE TRIGGER new_order
INSTEAD OF INSERT ON kzc.new_order
FOR EACH ROW
EXECUTE FUNCTION kzc.new_order()
However, this code makes a new ordergroup for every order that is in the compound insert. How can I make it so that my code only makes one new ordergroup entry and assigns its id to all orders?
Thanks in advance!
I suggest that you add an order_group_id column to the new_order view and create a sequence for it. Then create a DEFAULT value for the column:
ALTER VIEW kzc.new_order
ALTER order_group_id SET DEFAULT currval('order_group_id_seq');
Add a BEFORE INSERT trigger FOR EACH STATEMENT that just calls nextval for the sequence. The currval calls will all pick up the same generated value.
Then you have that number in your trigger and can use it as a primary key for order_group.
To avoid adding the row multiple times, use
INSERT INTO kzc.order_group (id, person)
VALUES (NEW.order_group_id, NEW.person)
ON CONFLICT (id) DO NOTHING;
Related
I want to create lists of items and prevent the entry of 2 identical lists, using a unique constraint on a computed column.
CREATE TABLE test_cc
(
list_id int,
list_item int,
list_items AS STRING_AGG(CONVERT(varchar(10), list_item),',') OVER (PARTITION BY list_id) WITHIN GROUP (ORDER BY list_item),
UNIQUE(bs)
);
INSERT INTO test_cc VALUES (1, 1),(1,2),(2,1),(2,2);
/*should not be possible.*/
Executing this on SQL Server 2019 returns Error Msg 4113 Level 16 during table creation.
Is declaring a unique constraint on an expression a good practice ?
My data volume for this table is not huge.
Making sure that lists are unique are difficult. As I mentioned in the comments you can't use aggregate function in a computed column; a computed column is a value calculated based on the row, not the table.
You also can't use an Indexed View with a UNIQUE INDEX on a STRING_AGG'd column, as STRING_AGG isn't allowed to be used in an indexed view.
One method, therefore, is to use a TRIGGER, however, this won't be performant; in fact as your table grows this is going to get increasingly slower. For a small dataset it should be fine.
CREATE TRIGGER dbo.UnqTrg_list_items_test_cc ON dbo.test_cc
AFTER INSERT,UPDATE,DELETE AS
BEGIN
IF EXISTS (SELECT 1
FROM (SELECT STRING_AGG(cc.list_item,',') WITHIN GROUP (ORDER BY cc.list_item) AS list_items
FROM dbo.test_cc cc
GROUP BY cc.list_id) SA
GROUP BY list_items
HAVING COUNT(list_items) > 1)
THROW 96432, N'Violation of Unique Trigger logic ''UnqTrg_list_items_test_cc''. Cannot insert duplicate list in object ''dbo.test_cc''. The statement has been aborted.',10;
END;
db<>fiddle demonstrating INSERT,DELETE and UPDATE failing.
I am trying to create a trigger function, to create a new row, in a table, when a value is modified or created in another table. But the problem is that I need to insert in the other table, the primary key that provoked the trigger function.
Is there a way to do it?
Basically, when an insert or update will be done in table 1, I want to see in table 2 a new row, with one field filed with the value of the primary key of the row in table1 that provoked the trigger.
begin
INSERT INTO resultados_infocorp(id_user, Procesado)
VALUES (<PRIMARY_KEY>,false)
RETURN NEW;
End;
This is because if Procesado is false, thank to the id_user I will make some validations, but the ID of the user is necesary and I cant do it from the backend of my project, because I have many db inputs.
PD: The primary key of the new table is a sequence, this is the reason why I am not passing this arg.
CREATE TRIGGER resultados_infocorp_actualizar
AFTER INSERT OR UPDATE OF id_user, fb_id, numdocumento, numtelefono, tipolicencia, trabajoaplicativo
ON public.usuarios
FOR EACH ROW
EXECUTE PROCEDURE public.update_solicitudes_infocorp();
You have not shown the trigger definition. Still if you want the PK value then something like:
INSERT INTO resultados_infocorp(id_user, Procesado)
VALUES (NEW.pk_fld,false)
Where pk_fld is the name of your PK field. Take a look here:
https://www.postgresql.org/docs/current/plpgsql-trigger.html
for what is available to a trigger function. For the purpose of this question the important part is:
NEW
Data type RECORD; variable holding the new database row for INSERT/UPDATE operations in row-level triggers. This variable is null in statement-level triggers and for DELETE operations.
I'm in trouble with the implementation of a trigger.
Assuming that I have two types:
CREATE TYPE customer_t AS OBJECT(
code INTEGER,
name VARCHAR(20),
surname VARCHAR(20),
age INTEGER);
and the type
CREATE TYPE ticket_t AS OBJECT (
price INTEGER,
cust REF customer_t
)
And then I have the associate tables:
CREATE TABLE customers OF TYPE customer_t
CREATE TABLE tickets OF TYPE ticket_t
I have to do an exercise so I have to create a trigger for ensure that a customer won't buy more than 10 tickets but, if I use command like "select count(*)" I get an error because I can't access to mutating table.
Please can anyone help me with this trigger?
EDIT:
I populated the tables as follows:
INSERT INTO custs (code, name, surname, age) values (123, 'Paolo', 'Past', 32);
and repeating the following operation ten times:
INSERT INTO tickets (price, cust) values
(4, (SELECT * FROM (SELECT REF(T) FROM custs T WHERE name = 'Paolo' AND surname = 'Past') WHERE rownum < 2))
The trigger implemented is:
create or replace
trigger check_num_ticket after insert on tickets
for each row
declare
num_ticket number;
begin
SELECT count(*) INTO num_ticket FROM tickets WHERE :new.cust = cust;
if (num_ticket >= 10) then
raise_application_error('-20099', 'no ticket available');
end if;
end;
And I get this error:
A trigger (or a user defined plsql function that is referenced in
this statement) attempted to look at (or modify) a table that was
in the middle of being modified by the statement which fired it.
You are getting the mutating table error, because you are inserting in the same table where you want to get the row count for. Imagine your insert statement inserts two rows. There is no rule which row to insert first and which last, but your trigger fires on one inserted row and wants to know how many rows are already in the table. The DBMS tells you this is undefined, as the table is currently mutating.
You need an after statement trigger instead of a before row trigger. So when the insert statement's inserts are done, you look at the table to see whether there are suddenly customers with too many rows in it.
(A great alternative is a compound trigger. It combines row and statement triggers. So in the after row section you'd remember the customers in some array/collection and in the after statement section you'd look up the table for only the remembered customers.)
I am trying to create a trigger that whenever you insert values inside a table called hotel, it takes some values from the field and inserts it inside another table called Restaurant.
My Hotel_ID is in sequence so I don't really give its value when I am using the insert statement to insert values inside the hotel table. Which creates problems for the restaurant table as it sets the value of Hotel_ID to null. I know in the insert statement I can just add the sequence name so that it works but the thing is, later on I have to convert my tables into APEX forms and with them, you can't insert the ID at all.
Anyway, here is my trigger that is basically supposed to take values from some fields of Hotel table and insert them into the Restaurant table:-
create or replace TRIGGER HOTELREST BEFORE INSERT ON HOTEL
FOR EACH ROW
BEGIN
IF INSERTING THEN
INSERT INTO RESTAURANT(CITY,ADDRESS,HOTEL_ID)
VALUES (:NEW.CITY,:NEW.ADDRESS,:NEW.HOTEL_ID);
END IF;
END;
Although the values of City and address get inserted inside the restaurant table, the value of hotel_id doesn't. Here is my insert statement for hotel:
INSERT INTO HOTEL(NAME,CITY,COUNTRY,ADDRESS,RATINGS)
VALUES ('Westin','Manchester','UK',5);
Now again, before you say that I didn't give an Id of the hotel, like I said, I am using sequence so when this row gets inserted inside the hotel table, a value for Hotel_Id is automatically generated. My trigger is also supposed to add Hotel_Id in my Restaurant table but it doesn't. It remains null. What do I do?
I'm trying to make a blog system of sort and I ran into a slight problem.
Simply put, there's 3 columns in my article table:
id SERIAL,
category VARCHAR FK,
category_id INT
id column is obviously the PK and it is used as a global identifier for all articles.
category column is well .. category.
category_id is used as a UNIQUE ID within a category so currently there is a UNIQUE(category, category_id) constraint in place.
However, I also want for category_id to auto-increment.
I want it so that every time I execute a query like
INSERT INTO article(category) VALUES ('stackoverflow');
I want the category_id column to be automatically be filled according to the latest category_id of the 'stackoverflow' category.
Achieving this in my logic code is quite easy. I just select latest num and insert +1 of that but that involves two separate queries.
I am looking for a SQL solution that can do all this in one query.
This has been asked many times and the general idea is bound to fail in a multi-user environment - and a blog system sounds like exactly such a case.
So the best answer is: Don't. Consider a different approach.
Drop the column category_id completely from your table - it does not store any information the other two columns (id, category) wouldn't store already.
Your id is a serial column and already auto-increments in a reliable fashion.
Auto increment SQL function
If you need some kind of category_id without gaps per category, generate it on the fly with row_number():
Serial numbers per group of rows for compound key
Concept
There are at least several ways to approach this. First one that comes to my mind:
Assign a value for category_id column inside a trigger executed for each row, by overwriting the input value from INSERT statement.
Action
Here's the SQL Fiddle to see the code in action
For a simple test, I'm creating article table holding categories and their id's that should be unique for each category. I have omitted constraint creation - that's not relevant to present the point.
create table article ( id serial, category varchar, category_id int )
Inserting some values for two distinct categories using generate_series() function to have an auto-increment already in place.
insert into article(category, category_id)
select 'stackoverflow', i from generate_series(1,1) i
union all
select 'stackexchange', i from generate_series(1,3) i
Creating a trigger function, that would select MAX(category_id) and increment its value by 1 for a category we're inserting a row with and then overwrite the value right before moving on with the actual INSERT to table (BEFORE INSERT trigger takes care of that).
CREATE OR REPLACE FUNCTION category_increment()
RETURNS trigger
LANGUAGE plpgsql
AS
$$
DECLARE
v_category_inc int := 0;
BEGIN
SELECT MAX(category_id) + 1 INTO v_category_inc FROM article WHERE category = NEW.category;
IF v_category_inc is null THEN
NEW.category_id := 1;
ELSE
NEW.category_id := v_category_inc;
END IF;
RETURN NEW;
END;
$$
Using the function as a trigger.
CREATE TRIGGER trg_category_increment
BEFORE INSERT ON article
FOR EACH ROW EXECUTE PROCEDURE category_increment()
Inserting some more values (post trigger appliance) for already existing categories and non-existing ones.
INSERT INTO article(category) VALUES
('stackoverflow'),
('stackexchange'),
('nonexisting');
Query used to select data:
select category, category_id From article order by 1,2
Result for initial inserts:
category category_id
stackexchange 1
stackexchange 2
stackexchange 3
stackoverflow 1
Result after final inserts:
category category_id
nonexisting 1
stackexchange 1
stackexchange 2
stackexchange 3
stackexchange 4
stackoverflow 1
stackoverflow 2
Postgresql uses sequences to achieve this; it's a different approach from what you are used to in MySQL. Take a look at http://www.postgresql.org/docs/current/static/sql-createsequence.html for complete reference.
Basically you create a sequence (a database object) by:
CREATE SEQUENCE serials;
And then when you want to add to your table you will have:
INSERT INTO mytable (name, id) VALUES ('The Name', NEXTVAL('serials')