postgresql – postgres INSERT触发器即使在ON CONFLICT DO NOTHING也会触发

在一些SO答案( 1,2)中,建议如果存在冲突并且ON CONFLICT DO nothing在触发语句中,则不应触发INSERT触发器.也许我误解了,但在我的实验中似乎并不是这样.

这是我的sql,在Postgres 9.6上运行.

CREATE TABLE t (
        n text PRIMARY KEY
);

CREATE FUNCTION def() RETURNS trigger AS $$
BEGIN
        RAISE NOTICE 'Called def()';
        RETURN NEW;
END;
$$LANGUAGE plpgsql;

CREATE TRIGGER deftrig BEFORE INSERT ON t FOR EACH ROW EXECUTE PROCEDURE def();

如果我然后运行几个插入：

testdb=> insert into t (n) values ('dummy') on conflict do nothing;
NOTICE:  Called def()
INSERT 0 1
testdb=> insert into t (n) values ('dummy') on conflict do nothing;
NOTICE:  Called def()
INSERT 0 0

我本来希望第一次见到Called def(),但不是第二次.

我错了什么？

解决方法

BEFORE INSERT触发器在冲突检查之前运行.触发器有机会更改插入的值,在此之前检查冲突是没有意义的.每 the documentation:

Note that the effects of all per-row BEFORE INSERT triggers are reflected in excluded values,since those effects may have contributed to the row being excluded from insertion.

AFTER INSERT触发器将按预期运行.