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 FOR1216MySQL_statements;

# changed

DECLARE foreign_key_error CONDITION FOR1216;

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  

CREATEPROCEDUREsp_add_location

(in_locationVARCHAR(30),

in_address1VARCHAR(30),

in_address2VARCHAR(30),

zipcodeVARCHAR(10),

OUTout_statusVARCHAR(30))

BEGIN

DECLARECONTINUEHANDLER

FOR1062

SETout_status='Duplicate Entry';

SETout_status='OK';

INSERTINTOlocations

(location,address1,address2,zipcode)

VALUES

(in_location,in_address1,in_address2,zipcode);

END;

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  

CREATEPROCEDUREsp_not_found()

READS SQL DATA

BEGIN

DECLAREl_last_rowINTDEFAULT0;

DECLAREl_dept_idINT:

DECLAREc_deptCURSORFOR

SELECTdepartment_idFROMdepartments;

DECLARECONTINUEHANDLERFORNOTFOUNDSETl_last_row=1;

OPENc_dept;

dept_cursor: LOOP

FETCHc_deptINTOl_dept_id;

IF (l_last_row=1)THEN

LEAVE dept_cursor;

ENDIF;

ENDLOOP dept_cursor;

CLOSEc_dept;

END;

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  

CREATEPROCEDUREsp_add_department

(p_department_nameVARCHAR(30),

p_manager_surnameVARCHAR(30),

p_manager_firstnameVARCHAR(30),

p_locationVARCHAR(30),

OUTp_sqlcodeINT,

OUTp_status_messageVARCHAR(100))

BEGIN

/* STARTDeclareConditions */

DECLAREduplicate_key CONDITIONFOR1062;

DECLAREforeign_key_violated CONDITIONFOR1216;

/*ENDDeclareCOnditions */

/* STARTDeclarevariablesandcursors */

DECLAREl_manager_idINT;

DECLAREcsr_mgr_idCURSORFOR

SELECTemployee_idFROMemployees

WHEREsurname=UPPER(p_manager_surname)

ANDfirstname=UPPER(p_manager_firstname);

/*ENDDeclarevariablesandcursors */

/* STARTDeclareException Handlers */

DECLARECONTINUEHANDLERFORduplicate_key

BEGIN

SETp_sqlcode=1052;

SETp_status_message='Duplicate key error';

END;

DECLARECONTINUEHANDLERFORforeign_key_violated

BEGIN

SETp_sqlcode=1216;

SETp_status_message='Foreign key violated';

END;

DECLARECONTINUEHANDLERFORNOTFOUND

BEGIN

SETp_sqlcode=1329;

SETp_status_message='No record found';

END;

/*ENDDeclareException Handlers */

/* START Execution */

SETp_sqlcode=0;

OPENcsr_mgr_id;

FETCHcsr_mgr_idINTOl_manager_id;

IF p_sqlcode<>0THEN/* Failedtoget manager id */

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

ELSE/* Got manager id, we can tryandinsert*/

INSERTINTOdepartments (department_name, manager_id, location)

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

IF p_sqlcode<>0THEN/* Failedtoinsertnew department */

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

ENDIF;

ENDIF;

CLOSEcsr_mgr_id;

/*ENDExecution */

END