begin;

create table test (
    id integer
);

insert into test(id) select generate_series(1,100);


create or replace function trg_check_max_4_updated_records() 
returns trigger as $$
declare
    counter_ integer := 0;
    tablename_ text := 'temptable';
begin
    raise notice 'trigger fired';
    select count(42) into counter_ 
        from pg_catalog.pg_tables where tablename = tablename_;
    if counter_ = 0 then
        raise notice 'Creating table %',tablename_;
        execute 'create temporary table ' || tablename_ || ' (counter integer) on commit drop';
        execute 'insert into ' || tablename_ || ' (counter) values(1)';

        execute 'select counter from ' || tablename_ into counter_;
        raise notice 'Actual value for counter= [%]',counter_;
    else
        execute 'select counter from ' || tablename_ into counter_;
        execute 'update ' || tablename_ || ' set counter = counter + 1';
        raise notice 'updating';
        execute 'select counter from ' || tablename_ into counter_;
        raise notice 'Actual value for counter= [%]',counter_;

        if counter_ > 4 then
            raise exception 'Cannot change more than 4 rows in one trancation';
        end if;

    end if;
    return new;
end; $$language plpgsql;


create trigger trg_bu_test before 
  update on test 
  for each row
  execute procedure trg_check_max_4_updated_records();

update test set id = 10 where id <= 1;
update test set id = 10 where id <= 2;
update test set id = 10 where id <= 3;
update test set id = 10 where id <= 4;
update test set id = 10 where id <= 5;

rollback;

主要思想是在“每行更新之前”触发,创建(如果需要)临时表(在事务结束时删除).在此表中只有一行具有一个值,即当前事务中更新的行数.对于每次更新,值都会递增.如果该值大于4,则停止事务.

但我认为这对你的问题是一个错误的解决方案.运行这样的错误查询有什么问题,你写了两次,所以你将改变8行.删除行或截断它们怎么样？