postgresql中的外键可以被触发器违反

到目前为止，我读到的所有内容似乎都表明，只有在插入数据时才会判断约束.(或在创建约束时)例如the manual on set constraints.

This makes sense and - if the database works properly - should be good enough. I'm still curious how I managed to circumvent this or if I just read the situation wrong and there was never a real constraint violation to begin with.

无论哪种情况，案件都已结案:-/

-------更新--------

肯定有违反约束的情况，是由错误的触发器引起的.下面是要复制的脚本:

-- Create master table
CREATE TABLE product
(
  id INT NOT NULL PRIMARY KEY
);

-- Create second table, referencing the first
CREATE TABLE example
(
  id int PRIMARY KEY REFERENCES product (id) ON DELETE CASCADE
);

-- Create a (broken) trigger function
--CREATE LANGUAGE plpgsql;
CREATE OR REPLACE FUNCTION delete_product()
  RETURNS trigger AS
$BODY$
    BEGIN
      DELETE FROM product WHERE product.id = OLD.id;
      -- This is an error!
      RETURN null;
    END;
$BODY$
  LANGUAGE plpgsql;

-- Add it to the second table
CREATE TRIGGER example_delete
  BEFORE DELETE
  ON example
  FOR EACH ROW
  EXECUTE PROCEDURE delete_product();

-- Now lets add a row
INSERT INTO product (id) VALUES (1);
INSERT INTO example (id) VALUES (1);

-- And now lets delete the row
DELETE FROM example WHERE id = 1;

/*
Now if everything is working, this should return two columns:
(pid,eid)=(1,1). However, it returns only the example id, so
(pid,eid)=(0,1). This means the foreign key constraint on the
example table is violated.
*/
SELECT product.id AS pid, example.id AS eid FROM product FULL JOIN example ON product.id = example.id;