创建用于在 postgres 中计算总和的触发器

Question

I have this tables in postgres

CREATE TABLE voting_option (
  id SERIAL PRIMARY KEY,
  -- SUM of all vote values for this voting option id
  votes_value INT NOT NULL DEFAULT 0
);
CREATE TABLE vote (
  id SERIAL PRIMARY KEY,
  voting_option_id INT NOT NULL,
  -- can be positive/negative or 0
  value INT NOT NULL
);

I want to create triggers that will automatically update votes_value every time I INSERT / UPDATE / DELETE a record to the vote table.

Something like this:

For INSERT: votes_value += vote.value

For DELETE: votes_value -= vote.value

For UPDATE: votes_value = votes_value - old vote.value + new vote.value

Answer 1

As @JimJones noticed, all you need is this simple view. You will have clean insert-only workflow as a bonus too instead of an update workflow in disguise.

create view voting_option_v as
 select voting_option_id id, sum(value) votes_value
 from vote 
 group by voting_option_id;