I am using dynamically created table partitions to store event information in a Postgresql 13 database. The master table from which the child tables inhert their structure contains an id field with an auto-incrementing sequence. The sequence, master table and trigger for inserts look as follows:
CREATE SEQUENCE event_id_seq
INCREMENT 1
START 1
MINVALUE 1
MAXVALUE 9223372036854775807
CACHE 1;
CREATE TABLE event_master
(
id bigint NOT NULL DEFAULT nextval('event_id_seq'::regclass),
event jsonb,
insert_time as timestamp
)
CREATE TRIGGER insert_event_trigger
BEFORE INSERT
ON event_master
FOR EACH ROW
EXECUTE PROCEDURE event_insert_function();
Additionally, the event_insert_function() uses the following code to insert new rows posted to the master table:
EXECUTE format('INSERT INTO %I (event, insert_time) VALUES($1,$2)', partition_name) using NEW.event, NEW.insert_time);
When looking at the sequence numbers in the id field, I only get every other number, i.e. 1,3,5,7, ...
Based on some related information I found, I assume this has something to do with Postgresql counting the initial insert into the master table and the triggered insert into the child table as two occurences. So my first question is, whether this is correct, and if so what's the rational behind it and why not "pass through" the insert from master to child?
More importantly though, what do I need to do to set up a properly incrementing sequence (i.e. returning 1,2,3,4 ...)?
Related
I have a table as follows
The table contains my application users and stores their clients. The column User Client ID refers to a foreign key linked to a different table that stores the clients details.
I need another column (User Client Counter) which is a just a counter of the clients of each user. I need it to start from 1 and goes up for each individual application user.
For the moment I'm populating this by counting the number of clients for each user + 1 before inserting a new row in the table :
select count(*) + 1 into MyVariable from Mytable where UserClientId = Something
Then I use MyVariable in the column User Client Counter
This methods works quite well, but in case the user is connected from two different sessions, the query may produce a wrong number of counts... in addition to that the performance may be bad in case of big tables...
Is there anyway better way to replace such process by using sequences ?
I've been looking to session sequences but there are reset after the end of each session.
(This column is a business need and cannot be replaced by something like rownumber in restitution queries. Since every client has to keep always the same identifier for the application user)
Thank you in advance.
Cheers,
I think you can just create a unique index on the app user and the running number:
create unique index idx on mytable (app_user_id, num);
And then insert with max + 1:
insert into mytable (app_user_id, client_id, num)
values
(
:app_user_id,
:client_id,
coalesce((select max(num) + 1 from mytable where app_user_id = :app_user_id), 1)
);
For this sort of requirement to be safe you will need to be able to lock rows at the right level so that you don't have two sessions that think the they are allowed to use the same value. The impact of this is that while one session is inserting a row for the 'Company X' user, another session will wait for the first user to commit if they're also trying to insert a row for 'Company X'.
This is super easy when you just have a table that stores information at the right level.
You can have a table of your users with a counter column which starts at 0.
MY_APPLICATION_USER CLIENT_COUNTER
-------------------------------------------------- --------------
Company X 1
Company Y 3
Company Z 1
As you insert rows into your main table, you update this table first setting the client_counter to be client_counter + 1 (you do this as one insert statement, no risky select then update!), then you return the updated value into your value for the client_id. This can all be done with a simple trigger.
create or replace trigger app_clients_ins
before insert
on app_clients
for each row
declare
begin
update app_users
set client_counter = client_counter + 1
where my_application_user = :new.my_application_user
return client_counter into :new.user_client_number;
end;
/
Of course, like any sequence if you delete a row it's not going to allow your next insert to fill that gap.
(db<>fiddle https://dbfiddle.uk/?rdbms=oracle_18&fiddle=7f1b4f4b6316d5983b921cae7b89317a )
if you want to have unique values to be inserted and there are chances that multiple users can insert rows into the same table at the same time then it is better to user Oracle Sequence.
CREATE SEQUENCE id_seq INCREMENT BY 1;
INSERT INTO Mytable(id) VALUES (id_seq.nextval);
In you case I think you want different sequence created for each Customer, How many different Customers you have, if you have in 100's then i don't think create sequence will work as you may have to create as many sequence .
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.
is it Possible to recover from a temporal table?
I defined 2 tables like this:
create table lib.x(
"ID" INTEGER GENERATED ALWAYS AS IDENTITY (
START WITH 1 INCREMENT BY 1
NO MINVALUE NO MAXVALUE
NO CYCLE NO ORDER
CACHE 20
),
char char(1),
row_start TIMESTAMP(12) NOT NULL GENERATED ALWAYS AS ROW BEGIN IMPLICITLY hidden,
row_end TIMESTAMP(12) NOT NULL GENERATED ALWAYS AS ROW END IMPLICITLY hidden,
row_id TIMESTAMP(12) GENERATED ALWAYS AS TRANSACTION START ID IMPLICITLY hidden,
PERIOD SYSTEM_TIME(row_start, row_end)
);
create table lib.x_history like lib.x;
alter TABLE lib.x
ADD VERSIONING USE HISTORY TABLE lib.x_history;
then I did this:
insert into lib.x(char) values('a'), ('b'), ('c');
delete from lib.x where id = 2;
Is it possible to restore the char 'b' with the ID 2?
Yes and no. It is not a system restore, but of course you can query the old state and use it to insert into the regular table. See the section "Querying system-period temporal data" in the Db2 docs.
You would first construct a query to search AS OF. Later, you could use it as input to an insert statement. Thus, you restore the value, but it is treated as deleting the value and inserting it as new.
I have a requirement as a trigger should get fired when any row is inserted or deleted from table FAB which contains num as unique value. and depending upon that num value, another table should be update.
e.g.
FAB table
num code trs
10 A2393 80
20 B3445 780
Reel table
reelnr num use flag
340345 10 500 1
when num 10 from FAB table gets deleted(or any new num gets inserted), the trigger should get fired and should check the reel table which contains that num value and give the reelnr.
How to proceed with this?
you can Use Inserted & Deleted Table in SQL
These two tables are special kind of table that are only available inside the scope of the triggers.
If you tries to use these tables outside the scope of Triggers then you will get Error.
Inserted : These table is use to get track of any new records that are insert in the table.
Suppose there are Six rows are inserted in your table then these table will consist of all the six rows that are inserted.
Deleted : These table is used to track all the Deleted record from your tables.
Last delete rows will be tracked by these table.
For Insert :
CREATE TRIGGER TR_AUDIT_Insert
ON Reel_table
FOR INSERT
AS
BEGIN
INSERT INTO Reel_table (reelnr, num, use, flag)
SELECT
reelnr,
num,
use,
flag
FROM
INSERTED
END
For Delete :
CREATE TRIGGER TR_AUDIT_Delete
ON Product
FOR DELETED
AS
BEGIN
INSERT INTO Reel_table (reelnr, num, use, flag)
SELECT
reelnr,
num,
use,
flag
FROM
DELETED
END
Note :
I don't know from where these three reelnr, use flag values you are getting
So, Please modify this as per your need.
This is the format of the Triggers that normally we use.
You also can do this by using single trigger also
I dont know what is your exact requirement
If you want to achieve by only single Trigger then you can refer this link :
Refer
I have the following problem, I want to have Composite Primary Key like:
PRIMARY KEY (`base`, `id`);
for which when I insert a base the id to be auto-incremented based on the previous id for the same base
Example:
base id
A 1
A 2
B 1
C 1
Is there a way when I say:
INSERT INTO table(base) VALUES ('A')
to insert a new record with id 3 because that is the next id for base 'A'?
The resulting table should be:
base id
A 1
A 2
B 1
C 1
A 3
Is it possible to do it on the DB exactly since if done programmatically it could cause racing conditions.
EDIT
The base currently represents a company, the id represents invoice number. There should be auto-incrementing invoice numbers for each company but there could be cases where two companies have invoices with the same number. Users logged with a company should be able to sort, filter and search by those invoice numbers.
Ever since someone posted a similar question, I've been pondering this. The first problem is that DBs don't provide "partitionable" sequences (that would restart/remember based on different keys). The second is that the SEQUENCE objects that are provided are geared around fast access, and can't be rolled back (ie, you will get gaps). This essentially this rules out using a built-in utility... meaning we have to roll our own.
The first thing we're going to need is a table to store our sequence numbers. This can be fairly simple:
CREATE TABLE Invoice_Sequence (base CHAR(1) PRIMARY KEY CLUSTERED,
invoiceNumber INTEGER);
In reality the base column should be a foreign-key reference to whatever table/id defines the business(es)/entities you're issuing invoices for. In this table, you want entries to be unique per issued-entity.
Next, you want a stored proc that will take a key (base) and spit out the next number in the sequence (invoiceNumber). The set of keys necessary will vary (ie, some invoice numbers must contain the year or full date of issue), but the base form for this situation is as follows:
CREATE PROCEDURE Next_Invoice_Number #baseKey CHAR(1),
#invoiceNumber INTEGER OUTPUT
AS MERGE INTO Invoice_Sequence Stored
USING (VALUES (#baseKey)) Incoming(base)
ON Incoming.base = Stored.base
WHEN MATCHED THEN UPDATE SET Stored.invoiceNumber = Stored.invoiceNumber + 1
WHEN NOT MATCHED BY TARGET THEN INSERT (base) VALUES(#baseKey)
OUTPUT INSERTED.invoiceNumber ;;
Note that:
You must run this in a serialized transaction
The transaction must be the same one that's inserting into the destination (invoice) table.
That's right, you'll still get blocking per-business when issuing invoice numbers. You can't avoid this if invoice numbers must be sequential, with no gaps - until the row is actually committed, it might be rolled back, meaning that the invoice number wouldn't have been issued.
Now, since you don't want to have to remember to call the procedure for the entry, wrap it up in a trigger:
CREATE TRIGGER Populate_Invoice_Number ON Invoice INSTEAD OF INSERT
AS
DECLARE #invoiceNumber INTEGER
BEGIN
EXEC Next_Invoice_Number Inserted.base, #invoiceNumber OUTPUT
INSERT INTO Invoice (base, invoiceNumber)
VALUES (Inserted.base, #invoiceNumber)
END
(obviously, you have more columns, including others that should be auto-populated - you'll need to fill them in)
...which you can then use by simply saying:
INSERT INTO Invoice (base) VALUES('A');
So what have we done? Mostly, all this work was about shrinking the number of rows locked by a transaction. Until this INSERT is committed, there are only two rows locked:
The row in Invoice_Sequence maintaining the sequence number
The row in Invoice for the new invoice.
All other rows for a particular base are free - they can be updated or queried at will (deleting information out of this kind of system tends to make accountants nervous). You probably need to decide what should happen when queries would normally include the pending invoice...
you can use the trigger for before insert and assign the next value by taking the max(id) with "base" filter which is "A" in this case.
That will give you the max(id) value as 2 and than increment it by max(id)+1. now push the new value to the "id" field. before insert.
I think this may help you
MSSQL Triggers: http://msdn.microsoft.com/en-in/library/ms189799.aspx
Test Table
CREATE TABLE MyTable
( base CHAR(1),
id INT
)
GO
Trigger Definition
CREATE TRIGGER dbo.tr_Populate_ID
ON dbo.MyTable
INSTEAD OF INSERT
AS
BEGIN
SET NOCOUNT ON;
INSERT INTO MyTable (base,id)
SELECT i.base, ISNULL(MAX(mt.id),0) +1 AS NextValue
FROM inserted i left join MyTable mt
on i.base = mt.base
GROUP BY i.base
END
Test
Execute the following statement multiple times and you will see the next values available in that group will be assigned to ID.
INSERT INTO MyTable VALUES
('A'),
('B'),
('C')
GO
SELECT * FROM MyTable
GO