CODEWITHSUNDEEP
sqlpostgresqlpartitioningdatabase-trigger
Tom
Tom

Reputation: 7951

PostgreSQL inherited table and insert triggers

I'm trying to follow the advice here to create a vertically partitioned table for storing time series data.

So far, my schema looks like this:

CREATE TABLE events 
(
     topic text, 
     t timestamp, 
     value integer, 
     primary key(topic, t)
);

CREATE TABLE events_2014 
(
     primary key (topic, t), 
     check (t between '2014-01-01' and '2015-01-01') 
) INHERITS (events);

Now I'm trying to create an INSTEAD OF INSERT trigger so that events can be inserted on the events table and the row will end up in the right sub-table. But the documentation says that INSTEAD OF INSERT triggers can only be created on views, not tables (or subtables):

CREATE OR REPLACE FUNCTION insert_events () RETURNS TRIGGER AS $insert_events$ BEGIN
  IF new.t between '2014-01-01' and '2015-01-01' THEN
    INSERT INTO events_2014 SELECT new.*;
  ...
  END IF
  RETURN NULL;
END;
$insert_events$ LANGUAGE PLPGSQL;

CREATE TRIGGER insert_events INSTEAD OF INSERT ON events FOR EACH ROW EXECUTE PROCEDURE insert_events();
ERROR:  "events" is a table
DETAIL:  Tables cannot have INSTEAD OF triggers.

What's the right way of doing this?

Upvotes: 2

Views: 2848

Answers (1)

Kamil Gosciminski
Kamil Gosciminski

Reputation: 17157

You need to declare BEFORE INSERT triggers.

Documentation on partitioning is a great source of knowledge in this matter and is full of examples.

Example function from docs

CREATE OR REPLACE FUNCTION measurement_insert_trigger()
RETURNS TRIGGER AS $$
BEGIN
    IF ( NEW.logdate >= DATE '2006-02-01' AND
         NEW.logdate < DATE '2006-03-01' ) THEN
        INSERT INTO measurement_y2006m02 VALUES (NEW.*);
    ELSIF ( NEW.logdate >= DATE '2006-03-01' AND
            NEW.logdate < DATE '2006-04-01' ) THEN
        INSERT INTO measurement_y2006m03 VALUES (NEW.*);
    ...
    ELSIF ( NEW.logdate >= DATE '2008-01-01' AND
            NEW.logdate < DATE '2008-02-01' ) THEN
        INSERT INTO measurement_y2008m01 VALUES (NEW.*);
    ELSE
        RAISE EXCEPTION 'Date out of range.  Fix the measurement_insert_trigger() function!';
    END IF;
    RETURN NULL;
END;
$$
LANGUAGE plpgsql;

Example trigger from docs

CREATE TRIGGER insert_measurement_trigger
    BEFORE INSERT ON measurement
    FOR EACH ROW EXECUTE PROCEDURE measurement_insert_trigger();

Returning NULL from BEFORE trigger will keep the parent table empty.

Upvotes: 5

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