在mysql触发器中引发错误

Here is one hack 这可能奏效。它不干净,但看起来可能有用:

实际上,您只需尝试更新不存在的列。

从MySQL5.5开始,您可以使用 SIGNAL syntax to throw an exception :

signal sqlstate '45000' set message_text = 'My Error Message';

状态45000是表示“未处理的用户定义异常”的一般状态。

下面是一个更完整的方法示例:

delimiter //
use test//
create table trigger_test
(
    id int not null
)//
drop trigger if exists trg_trigger_test_ins //
create trigger trg_trigger_test_ins before insert on trigger_test
for each row
begin
    declare msg varchar(128);
    if new.id < 0 then
        set msg = concat('MyTriggerError: Trying to insert a negative value in trigger_test: ', cast(new.id as char));
        signal sqlstate '45000' set message_text = msg;
    end if;
end
//

delimiter ;
-- run the following as seperate statements:
insert into trigger_test values (1), (-1), (2); -- everything fails as one row is bad
select * from trigger_test;
insert into trigger_test values (1); -- succeeds as expected
insert into trigger_test values (-1); -- fails as expected
select * from trigger_test;

不幸的是,@ruidc提供的答案在5.5之前的MySQL版本中不起作用,因为没有实现 信号 用于存储过程。

我的解决方案 found 是模拟一个信号 table_name doesn't exist 错误,将自定义错误消息推送到 table_name .

黑客可以使用触发器或存储过程来实现。我按照@ruidc使用的示例描述下面的两个选项。

使用触发器

DELIMITER $$
-- before inserting new id
DROP TRIGGER IF EXISTS before_insert_id$$
CREATE TRIGGER before_insert_id
    BEFORE INSERT ON test FOR EACH ROW
    BEGIN
        -- condition to check
        IF NEW.id < 0 THEN
            -- hack to solve absence of SIGNAL/prepared statements in triggers
            UPDATE `Error: invalid_id_test` SET x=1;
        END IF;
    END$$

DELIMITER ;

使用存储过程

存储过程允许您使用动态SQL,这使得在一个过程中封装错误生成功能成为可能。相反,我们应该控制应用程序的插入/更新方法,因此它们只使用我们的存储过程(不授予插入/更新的直接特权)。

DELIMITER $$
-- my_signal procedure
CREATE PROCEDURE `my_signal`(in_errortext VARCHAR(255))
BEGIN
    SET @sql=CONCAT('UPDATE `', in_errortext, '` SET x=1');
    PREPARE my_signal_stmt FROM @sql;
    EXECUTE my_signal_stmt;
    DEALLOCATE PREPARE my_signal_stmt;
END$$

CREATE PROCEDURE insert_test(p_id INT)
BEGIN
    IF NEW.id < 0 THEN
         CALL my_signal('Error: invalid_id_test; Id must be a positive integer');
    ELSE
        INSERT INTO test (id) VALUES (p_id);
    END IF;
END$$
DELIMITER ;

以下过程(在mysql5上)是抛出自定义错误并同时记录它们的一种方法:

create table mysql_error_generator(error_field varchar(64) unique) engine INNODB;
DELIMITER $$
CREATE PROCEDURE throwCustomError(IN errorText VARCHAR(44))
BEGIN
    DECLARE errorWithDate varchar(64);
    select concat("[",DATE_FORMAT(now(),"%Y%m%d %T"),"] ", errorText) into errorWithDate;
    INSERT IGNORE INTO mysql_error_generator(error_field) VALUES (errorWithDate);
    INSERT INTO mysql_error_generator(error_field) VALUES (errorWithDate);
END;
$$
DELIMITER ;


call throwCustomError("Custom error message with log support.");

CREATE TRIGGER sample_trigger_msg 
    BEFORE INSERT
FOR EACH ROW
    BEGIN
IF(NEW.important_value) < (1*2) THEN
    DECLARE dummy INT;
    SELECT 
           Enter your Message Here!!!
 INTO dummy 
        FROM mytable
      WHERE mytable.id=new.id
END IF;
END;

另一种(黑客)方法(如果您出于某种原因不在5.5+上),您可以使用:

如果您有一个必需的字段,那么在触发器内,将必需的字段设置为一个无效的值,如NULL。这对插入和更新都有效。请注意,如果空值是必需字段的有效值(出于某种疯狂的原因),则此方法将不起作用。

BEGIN
    -- Force one of the following to be assigned otherwise set required field to null which will throw an error
    IF (NEW.`nullable_field_1` IS NULL AND NEW.`nullable_field_2` IS NULL) THEN
        SET NEW.`required_id_field`=NULL;
    END IF;
END

如果您在5.5+上,则可以使用其他答案中描述的信号状态:

BEGIN
    -- Force one of the following to be assigned otherwise use signal sqlstate to throw a unique error
    IF (NEW.`nullable_field_1` IS NULL AND NEW.`nullable_field_2` IS NULL) THEN
        SIGNAL SQLSTATE '45000' set message_text='A unique identifier for nullable_field_1 OR nullable_field_2 is required!';
    END IF;
END