mysql 触发器在插入触发器之前不强制执行

Question

我正在尝试强制执行独特的约束。我有两个表，有一个公共列 puuid。两者的价值都是独一无二的。如果用户尝试将 puuid 插入 table1 并且该 puuid 已存在于 table2 中，则应该阻止我这样做。我无法让它工作。这是我的查询：

create table if not exists table1
(puuid varchar(50) not null unique)

create table if not exists table2
(puuid varchar(50) not null unique)

delimiter $$
create trigger temp_trigger
before INSERT
on table2 t2 for each ROW 
BEGIN 
    declare c int,
    select count(*) into c from table1 t1 where t1.puuid = NEW.puuid
    if (c > 0) THEN 
    -- abort insert because puuid cannot be null
    set NEW.puuid = NULL;
    end if;
    
END$$

delimiter;

insert into table1 (puuid)
values ('22')

insert into table2 (puuid)
values ('22')

仍然插入成功。我究竟做错了什么？

Answer 1

您的代码有一些错误，更正了代码，使之符合您的需要

但更好的方法是使用SIGNAL 语句

查看第二个触发器

create table if not exists table1
(puuid varchar(50) not null unique);

create table if not exists table2
(puuid varchar(50) not null unique);
create table if not exists table3
(puuid varchar(50) not null unique)

create trigger temp_trigger
before INSERT
on table2  for each ROW 
BEGIN 
    declare c int;
    select count(*) into c from table1 t1 where t1.puuid = NEW.puuid;
    if (c > 0) THEN 
    -- abort insert because puuid cannot be null
    set NEW.puuid = NULL;
    end if;
    
END;

insert into table1 (puuid)
values ('22');

insert into table2 (puuid)
values ('22')

列“puuid”不能为空

create trigger temp_trigger2
before INSERT
on table3  for each ROW 
BEGIN 
    declare c int;
    select count(*) into c from table1 t1 where t1.puuid = NEW.puuid;
    if (c > 0) THEN 
        SIGNAL SQLSTATE '45000'
          SET MESSAGE_TEXT = 'id already exists';
    end if;
    
END;

insert into table3 (puuid)
values ('22')

id已经存在

SELECT * FROM table1;

| 普乌伊德 |
| :----|
| 22 | 22

SELECT * FROM table2;

| 普乌伊德 |
| :----|

SELECT * FROM table3;

| 普乌伊德 |
| :----|

db<>在这里摆弄