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;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