postgresql - postgresql 中的更新语句后未触发规则

Question

按照 www.postgresql.org 中的指南进行操作

我创建了这个语句:

CREATE TABLE shoelace_log (
sl_name    text,          -- shoelace changed
sl_avail   integer,       -- new available value
log_who    text,          -- who did it
log_when   timestamp      -- when);
CREATE RULE log_shoelace AS ON UPDATE TO shoelace_data
WHERE NEW.sl_avail <> OLD.sl_avail
DO INSERT INTO shoelace_log VALUES (
                                NEW.sl_name,
                                NEW.sl_avail,
                                current_user,
                                current_timestamp
                            );

当我尝试在 pgAdmin3 查询控制台中执行查询时:

UPDATE shoelace_data SET sl_avail = 6 WHERE sl_name = 'sl7';

只执行更新查询，不触发规则。我尝试使用 EXPLAIN 命令来理解原因。

EXPLAIN UPDATE shoelace_log SET sl_avail = 6 WHERE sl_name = 'sl7';

日志说:

"Seq Scan on shoelace_log  (cost=0.00..19.66 rows=4 width=32)"
"  Filter: (sl_name = 'sl7'::text)"
"Seq Scan on shoelace_log  (cost=0.00..19.62 rows=4 width=78)"
"  Filter: (sl_name = 'sl7'::text)"

我也尝试在 EXPLAIN 中使用 VERBOSE 选项，但我不明白为什么我的事件没有被触发。

Answer 1

您选择了错误的功能。完全忘记规则——它们很难，几乎不可能正确地做。

这里你需要的是一个触发器:

create or replace function shoelace_log_who_when()
returns trigger language plpgsql as
$$
begin
  if OLD.sl_avail is distinct from NEW.sl_avail then
    NEW.log_who = current_user;
    NEW.log_when = current_timestamp;
  end if;
  return NEW;
end;
$$;

create trigger shoelace_log_who_when before update on shoelace_log
  for each row execute procedure shoelace_log_who_when();

试一试:

insert into shoelace_log values ( 'foo', 1, NULL, NULL );select * from shoelace_log;

sl_name | sl_avail | log_who | log_when ---------+----------+---------+----------foo     |        1 |         | 

update shoelace_log set sl_avail=2;select * from shoelace_log;

 sl_name | sl_avail | log_who  |         log_when          ---------+----------+----------+--------------------------- foo     |        2 | tometzky | 2011-03-30 17:06:21.07137