So, I think this should be fairly simple, but the documentation makes it seem somewhat more complicated. I've written an SQL function in PostgreSQL (8.1, for now) which does some cleanup on some string input. For what it's worth, the string is an LDAP distinguished name, and I want there to consistently be no spaces after the commas - and the function is clean_dn(), which returns the cleaned DN. I want to do the same thing to force all input to another couple of columns to lower case, etc - which should be easy once I figure this part out.
Anyway, I want this function to be run on the "dn" column of a table any time anyone attempts to insert to or update and modify that column. But all the rule examples I can find seem to make the assumption that all insert/update queries modify all the columns in a table all the time. In my situation, that is not the case. What I think I really want is a constraint which just changes the value rather than returning true or false, but that doesn't seem to make sense with the SQL idea of a constraint. Do I have my rule do an UPDATE into the NEW table? Do I have to create a new rule for every possible combination of NEW values? And if I add a column, do I have to go through and update all of my rule combinations to refelect every possible new combination of columns?
There has to be an easy way...
First, update to a current version of PostgreSQL. 8.1 is long dead and forgotten und unsupported and very, very old .. you get my point? Current version is PostgreSQL 9.2.
Then, use a trigger instead of a rule. It's simpler. It's the way most people go. I do.
For column col in table tbl ...
First, create a trigger function:
CREATE OR REPLACE FUNCTION trg_tbl_insupbef()
RETURNS trigger AS
$BODY$
BEGIN
NEW.col := f_myfunc(NEW.col); -- your function here, must return matching type
RETURN NEW;
END;
$BODY$
LANGUAGE plpgsql VOLATILE;
Then use it in a trigger.
For ancient Postgres 8.1:
CREATE TRIGGER insupbef
BEFORE INSERT OR UPDATE
ON tbl
FOR EACH ROW
EXECUTE PROCEDURE trg_tbl_insupbef();
For modern day Postgres (9.0+)
CREATE TRIGGER insbef
BEFORE INSERT OR UPDATE OF col -- only call trigger, if column was updated
ON tbl
FOR EACH ROW
EXECUTE PROCEDURE trg_tbl_insupbef();
You could pack more stuff into one trigger, but then you can't condition the UPDATE trigger on just the one column ...
Related
I have a table where I would like to calculate the difference in time (in hours) between two columns after inserting a row. I would like to set up a trigger to do this whenever an insert or update is performed on the table.
My columns are delay_start, delay_stop, and delay_duration. I would like to do the following:
delay_duration = delay_stop - delay_start
The result should be of numeric (4,2) value and go into the delay_duration category. Below is what I have so far, but it will not populate the column for some reason.
BEGIN
INSERT INTO public.deckdelays(delay_duration)
VALUES(DATEDIFF(hh, delay_stop, delay_start));
RETURN NEW;
END;
I am quite new to all of this so if anyone could help I would greatly appreciate it!
If you have Postgres 12 or later you can define delay_duration as a generated column. This allows you to eliminate triggers.
create table deckdelays(id integer generated always as identity
, delay_start timestamp
, delay_stop timestamp
, delay_duration numeric(4,2)
generated always as
( extract(epoch from (delay_stop - delay_start))/3600 )
stored
--, other attributes
);
See demo here.
But if you insist on a trigger:
create or replace
function delayduration_func()
returns trigger
language plpgsql
as $$
begin
new.delay_duration = (extract(epoch from (deckdelays.delay_stop - deckdelays.delay_start))/3600)::numeric;
return new;
end;
$$;
create trigger delaydurationset1
before insert
or update of delay_stop, delay_start
on deckdelays
execute procedure delayduration_func();
Changes:
Before trigger instead of after. A before trigger can modify the
values in a column without additional DML statements, an after
trigger cannot. Issuing a DML statement on a table within a trigger
on that same table can lead to all types of problems. It is bast
avoided if possible.
Trigger name and function name not the same. Might just be me but I
do not like different things having the same name. Although it works
often leads to confusion. Always avoid confusion if possible.
Trigger fires on update of delay_start. An update of either delay_start or delay_end also updates delay_duration.
I'm bringing in data from Excel into a PostgreSQL Db. There's a lot wrong with this data, but one thing that seems to connect several tables is a customer_id.
However, in the customer table I've a unique char(8) that always has a leading zero. Yes, if it were up to me I'd enforce this data weren't so screwy upstream, but I'm dealing with sales folks here, manufacturing there, financing, etc.
And, the customer id ALMOST matches through these various sources! It is just that the customer_id some data doesn't have the leading zero, so customers.id = '01234567' does represent orders.customer_id = '1234567'.
I'm using COPY command in Postgres, which is a new thing to me. Unfortunately, I cannot define a foreign key relationship on customer.id because of this small discrepancy.
How would I do a COPY and tell the column value to add a leading zero? Is this possible? I'm hoping I can do it right in the COPY statement? Thanks for any insight in how to do this!
EDIT:
A comment lead me to this documentation. I'll update with an answer after I figure this out. Looks like an ON BEFORE INSERT is what I'll need.
CREATE TRIGGER trigger_name
{BEFORE | AFTER} { event }
ON table_name
[FOR [EACH] { ROW | STATEMENT }]
EXECUTE PROCEDURE trigger_function
I'm the original poster and this is the answer to my question. I was bringing in data from XLS to PG and the leading zeros on customer_id(s) were dropped when exporting XLS to CSV for a COPY into PG.
Thanks be to an answer here that really pointed me down the right path: Postgresql insert trigger to set value
-- create table
CREATE TABLE T (customer_id char(8));
-- draft function to be used by trigger. NOTE the double single quotes.
CREATE FUNCTION lpad_8_0 ()
RETURNS trigger AS '
BEGIN
NEW.customer_id := (SELECT LPAD(NEW.customer_id, 8, ''0''));
RETURN NEW;
END' LANGUAGE 'plpgsql';
-- setup on before insert trigger to execute lpad_8_0 function
CREATE TRIGGER my_on_before_insert_trigger
BEFORE INSERT ON T
FOR EACH ROW
EXECUTE PROCEDURE lpad_8_0();
-- some sample inserts
INSERT INTO T
VALUES ('1234'), ('7');
Here's a working fiddle: http://sqlfiddle.com/#!17/a176e/1/0
NOTE: If the value here were larger than char(8) the COPY will still fail.
i want an upsert functionality that returns the (new/existing) id of the row.
Linking to my previous question. I asked previously about RULE postgres create rule on insert do nothing if exists insert otherwise; RETURNING id but looks like it is not possible.
So I resort to a trigger
CREATE OR REPLACE FUNCTION upsert_asset() RETURNS trigger AS $trigger_bound$
BEGIN
INSERT INTO asset(symbol, name, type, status)
VALUES (NEW.symbol, NEW.name, NEW.type, NEW.status)
ON CONFLICT (symbol) DO UPDATE SET symbol = EXCLUDED.symbol;
RETURN NEW;
END;
$trigger_bound$
LANGUAGE plpgsql;
CREATE OR REPLACE TRIGGER upsert_asset_trigger
AFTER INSERT ON asset
FOR EACH ROW
EXECUTE PROCEDURE upsert_asset();
I tested the above and works. So my questions are
Is this trigger a correct way to achieve this functionality? Any race conditions/performance issues that i should know about?
How can I generalize this query, by not giving the column names? asset(symbol, name, type, status). i do not want to pay attention to this rule every time I change my table. Is it possible to say NEW.* or column.* or something? What psuedorelations are available to achieve this? Please note there are some default columns too. So how does NEW.default_column get a value incase the insert statement has left that column in the insert statement?
Thanks,
So I am working on adding a last updated time to the database for my app's server. The idea is that it will record the time an update is applied to one of our trips and then the app can send a get request to figure out if it's got all of the correct up to date information.
I've added the column to our table, and provided the service for it all, and finally manage to get a trigger going to update the column every time a change is made to a trip in it's trip table. My problem now comes from the fact that the information that pertains to a trip is stored across a multitude of other tables as well (for instance, there are tables for the routes that make up a trip and the photos that a user can see on the trip, etc...) and if any of that data changes, then the trip's update time also needs to change. I can't for the life of me figure out how to set up the trigger so that when I change some route information, the last updated time for the trip(s) the route belongs to will be updated in it's table.
This is my trigger code as it stands now: it updates the trip table's last updated column when that trip's row is updated.
CREATE OR REPLACE FUNCTION record_update_time() RETURNS TRIGGER AS
$$
BEGIN
NEW.last_updated=now();
RETURN NEW;
END;
$$
LANGUAGE PLPGSQL;
CREATE TRIGGER update_entry_on_entry_change
BEFORE UPDATE ON mydatabase.trip FOR EACH ROW
EXECUTE PROCEDURE record_update_time();
--I used the next two queries just to test that the trigger works. It
--probably doesn't make a difference to you but I'll keep it here for reference
UPDATE mydatabase.trip
SET title='Sample New Title'
WHERE id = 2;
SELECT *
FROM mydatabase.trip
WHERE mydatabase.trip.id < 5;
Now I need it to update when the rows referencing the trip row with a foreign key get updated. Any ideas from someone more experienced with SQL triggers than I?
"mydatabase" is a remarkably unfortunate name for a schema.
The trigger function could look like this:
CREATE OR REPLACE FUNCTION trg_upaft_upd_trip()
RETURNS trigger
LANGUAGE plpgsql AS
$func$
BEGIN
UPDATE mydatabase.trip t -- "mydatabase" = schema name (?!)
SET last_updated = now()
WHERE t.id = NEW.trip_id -- guessing column names
RETURN NULL; -- calling this AFTER UPDATE
END
$func$;
And needs to be used in a trigger on every related table (not on trip itself):
CREATE TRIGGER upaft_upd_trip
AFTER UPDATE ON mydatabase.trip_detail
FOR EACH ROW EXECUTE PROCEDURE trg_upaft_upd_trip();
You also need to cover INSERT and DELETE (and possibly COPY) on all sub-tables ...
This approach has many potential points of failure. As alternative, consider a query or view that computes the latest last_updated from sub-tables dynamically. If you update often this might be the superior approach.
If you rarely UPDATE and SELECT often, your first approach might pay.
I'm writing three triggers in PL/pgSQL. In each case, I have a RECORD variable and want to insert that into a table, delete it from the table, or update it to represent a second RECORD variable.
Adding is easy: INSERT INTO mytable VALUES (NEW.*);
Deleting isn't as easy, there doesn't seem to be a syntax for something like this:
DELETE FROM mytable
WHERE * = OLD.*;
Updating has the same problem. Is there an easy solution, short of generating matching SQL queries that compare each attribute using ideas from this answer?
You can use a trick for delete
create table t(a int, b int);
create table ta(a int, b int);
create function t1_delete()
returns trigger as $$
begin
delete from ta where ta = old;
return null;
end
$$ language plpgsql;
But this trick doesn't work for UPDATE. So fully simple trigger in PL/pgSQL is not possible simply.
You write about a record variable and it is, indeed, not trivial to access individual columns of an anonymous record in plpgsql.
However, in your example, you only use OLD and NEW, which are well known row types, defined by the underlying table. It is trivial to access individual columns in this case.
DELETE FROM mytable
WHERE mytable_id = OLD.mytable_id;
UPDATE mytable_b
SET some_col = NEW.some_other_col
WHERE some_id = NEW.mytable_id;
Etc.
Just be careful not to create endless loops.
In case you just want to "update" columns of the current row, you can simply assign to columns the NEW object in the trigger. You know that, right?
NEW.some_col := 'foo';
Dynamic column names
If you don't know column names beforehand, you can still do this generically with dynamic SQL as detailed in this related answer:
Update multiple columns in a trigger function in plpgsql