如何在MySQL函数中引发错误

Question

我已经创建了一个MySQL函数,并且如果为参数传递的值无效,则会引发错误.在MySQL函数中引发错误的选项有哪些？

Answer 1

MySQL 5.5引入了信号,类似于其他语言中的异常:

http://dev.mysql.com/doc/refman/5.5/en/signal.html

例如,在mysql命令行客户端中:

mysql> SIGNAL SQLSTATE '45000' SET MESSAGE_TEXT = 'Custom error';
ERROR 1644 (45000): Custom error

Answer 2

它实际上是所有三个答案的组合.您调用一个不存在的过程来引发错误,然后声明一个捕获您生成的错误的退出处理程序.下面是一个示例,如果要删除的行设置了外键ID,则使用SQLSTATE 42000(过程不存在)在删除之前抛出错误:

DROP PROCEDURE IF EXISTS decount_test;

DELIMITER //

CREATE DEFINER = 'root'@'localhost' PROCEDURE decount_test ( p_id bigint )
DETERMINISTIC MODIFIES SQL DATA
BEGIN
  DECLARE EXIT HANDLER FOR SQLSTATE '42000'
    SELECT 'Invoiced barcodes may not have accounting removed.';
  IF (SELECT invoice_id 
       FROM accounted_barcodes
       WHERE id = p_id
    ) THEN
    CALL raise_error;
 END IF;
 DELETE FROM accounted_barcodes WHERE id = p_id;
END //

DELIMITER ;

输出:

call decount_test(123456);
+----------------------------------------------------+
| Invoiced barcodes may not have accounting removed. |
+----------------------------------------------------+
| Invoiced barcodes may not have accounting removed. | 
+----------------------------------------------------+

Answer 3

为什么不在VARCHAR声明的INTEGER变量中存储？

DELIMITER $$ DROP FUNCTION IF EXISTS `raise_error` $$
CREATE FUNCTION `raise_error`(MESSAGE VARCHAR(255)) 
RETURNS INTEGER DETERMINISTIC BEGIN
  DECLARE ERROR INTEGER;
  set ERROR := MESSAGE;
  RETURN 0;
END $$ DELIMITER ;
-- set @foo := raise_error('something failed'); -- or within a query

错误信息是:

不正确的整数值:第1行的列'ERROR''失败'

它并不完美,但它提供了一个非常具有描述性的消息,您不必编写任何扩展DLL.

Answer 4

在MySQL 5中,您可能通过调用不存在的存储过程(CALL raise_error)或将无效值传递给查询(如null到NOT NULL约束字段)来引发错误.以下是Roland Bouman关于在MySQL函数中引发错误的有趣帖子:

http://rpbouman.blogspot.com/2005/11/using-udf-to-raise-errors-from-inside.html

Answer 5

您必须定义异常处理程序。看看http://dev.mysql.com/doc/refman/5.0/en/declare-handler.html