Mysql 异常处理流程

mysql存储过程也提供了对异常处理的功能：通过定义HANDLER来完成异常声明的实现

语法如下：

DECLARE handler_type HANDLER FOR condition_value[,...] sp_statement handler_type: CONTINUE | EXIT condition_value: SQLSTATE [VALUE] sqlstate_value | condition_name | SQLWARNING | NOT FOUND | SQLEXCEPTION
| mysql_error_code

Handlers类型:

1, EXIT: 发生错误时退出当前代码块（可能是子代码块或者main代码块） 2, CONTINUE: 发送错误时继续执行后续代码

condition_value：

condition_value支持标准的SQLSTATE定义；

SQLWARNING是对所有以01开头的SQLSTATE代码的速记

NOT FOUND是对所有以02开头的SQLSTATE代码的速记

SQLEXCEPTION是对所有没有被SQLWARNING或NOT FOUND捕获的SQLSTATE代码的速记

除了SQLSTATE值，MySQL错误代码也被支持

但是对于mysql而言，优先级如下： MySQL Error code > SQLSTATE code > 命名条件

使用SQLSTATE还是MySQL Error Code？

1，SALSTATE是标准，貌似会更portable，但是实际上MySQL、DB2、Oracle等等的存储程序语法大相径庭，所以portable的优势不存在
2，MySQL error code与SQLSTATE并不是一一对应的，比如很多MySQL error code都映射到同一SQLSTATE code(HY000)

当MySQL客户端碰到错误时，它会报告MySQL
error code和相关的SQLSATE code:

mysql
> CALL nosuch_sp(); ERROR 1305 (42000): PROCEDURE sqltune.nosuch_sp does not exist

具体的sqlsdate和mysql
error code的对应可以在http://dev.mysql.com/doc/的MySQL
reference manual的附录B找到完整的最新的error codes

condition_name：命名条件

MySQL
error code或者SQLSTATE code的可读性太差，所以引入了命名条件:

语法：

Java代码







DECLARE condition_name CONDITION FOR condition_value condition_value: SQLSTATE [VALUE] sqlstate_value | mysql_error_code

DECLARE condition_name CONDITION FOR condition_value

condition_value:
SQLSTATE [VALUE] sqlstate_value
| mysql_error_code

使用:

Java代码







# original DECLARE CONTINUE HANDLER FOR 1216 MySQL_statements; # changed DECLARE foreign_key_error CONDITION FOR 1216; DECLARE CONTINUE HANDLER FOR foreign_key_error MySQL_statements;

# original
DECLARE CONTINUE HANDLER FOR 1216 MySQL_statements;

# changed
DECLARE foreign_key_error CONDITION FOR 1216;
DECLARE CONTINUE HANDLER FOR foreign_key_error MySQL_statements;

用condition_name为错误代码起了个别名。

示例1：Duplicate entry Handler

Sql代码

CREATE PROCEDURE sp_add_location
(in_location    VARCHAR(30),
in_address1    VARCHAR(30),
in_address2    VARCHAR(30),
zipcode        VARCHAR(10),
OUT out_status VARCHAR(30))
BEGIN
DECLARE CONTINUE HANDLER
FOR 1062
SET out_status='Duplicate Entry';

SET out_status='OK';
INSERT INTO locations
(location,address1,address2,zipcode)
VALUES
(in_location,in_address1,in_address2,zipcode);
END;

示例2： Last Row Handler

Sql代码

CREATE PROCEDURE sp_not_found()
READS SQL DATA
BEGIN
DECLARE l_last_row INT DEFAULT 0;
DECLARE l_dept_id INT:
DECLARE c_dept CURSOR FOR
SELECT department_id FROM departments;
DECLARE CONTINUE HANDLER FOR NOT FOUND SET l_last_row=1;

OPEN c_dept;
dept_cursor: LOOP
FETCH c_dept INTO l_dept_id;
IF (l_last_row=1) THEN
LEAVE dept_cursor;
END IF;
END LOOP dept_cursor;
CLOSE c_dept;
END;

综合示例：

Sql代码







CREATE PROCEDURE sp_add_department
(p_department_name VARCHAR(30),
p_manager_surname VARCHAR(30),
p_manager_firstname VARCHAR(30),
p_location VARCHAR(30),
OUT p_sqlcode INT,
OUT p_status_message VARCHAR(100))
BEGIN

/* START Declare Conditions */

DECLARE duplicate_key CONDITION FOR 1062;
DECLARE foreign_key_violated CONDITION FOR 1216;

/* END Declare COnditions */

/* START Declare variables and cursors */

DECLARE l_manager_id INT;
DECLARE csr_mgr_id CURSOR FOR
SELECT employee_id FROM employees
WHERE surname=UPPER(p_manager_surname)
AND firstname=UPPER(p_manager_firstname);

/* END Declare variables and cursors */

/* START Declare Exception Handlers */

DECLARE CONTINUE HANDLER FOR duplicate_key

BEGIN
SET p_sqlcode=1052;
SET p_status_message='Duplicate key error';
END;

DECLARE CONTINUE HANDLER FOR foreign_key_violated

BEGIN
SET p_sqlcode=1216;
SET p_status_message='Foreign key violated';
END;

DECLARE CONTINUE HANDLER FOR NOT FOUND

BEGIN
SET p_sqlcode=1329;
SET p_status_message='No record found';
END;

/* END Declare Exception Handlers */

/* START Execution */

SET p_sqlcode=0;
OPEN csr_mgr_id;
FETCH csr_mgr_id INTO l_manager_id;

IF p_sqlcode<>0 THEN /* Failed to get manager id */

SET p_status_message=CONCAT(p_status_message,' when fetching manager id');

ELSE /* Got manager id, we can try and insert */

INSERT INTO departments (department_name, manager_id, location)

VALUES(UPPER(p_department_name), l_manager_id, UPPER(p_location));

IF p_sqlcode<>0 THEN /* Failed to insert new department */

SET p_status_message=CONCAT(p_status_message, ' when inserting new department');

END IF;
END IF;

CLOSE csr_mgr_id;

/* END Execution */

END