mysql存储过程之异常处理篇

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：

DECLARE condition_name CONDITION FOR condition_value

condition_value:
    SQLSTATE [VALUE] sqlstate_value
  | mysql_error_code

 使用: 

# 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

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

 

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：

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